Method and apparatus for capacitive deionization and electrochemical purification and regeneration of electrodes

ABSTRACT

An electrically regeneratable electrochemical cell (30) for capacitive deionization and electrochemical purification and regeneration of electrodes includes two end plates (31, 32), one at each end of the cell (30). Two end electrodes (35, 36) are arranged one at each end of the cell (30), adjacent to the end plates (31, 32). An insulator layer (33) is interposed between each end plate (31, 32) and the adjacent end electrode (35, 36). Each end electrode (35, 36) includes a single sheet (44) of conductive material having a high specific surface area and sorption capacity. In one embodiment, the sheet (44) of conductive material is formed of carbon aerogel composite. The cell (30) further includes a plurality of generally identical double-sided intermediate electrodes (37-43) that are equidistally separated from each other, between the two end electrodes (35, 36). As the electrolyte enters the cell, it flows through a continuous open serpentine channel (65-71) defined by the electrodes, substantially parallel to the surfaces of the electrodes. By polarizing the cell (30), ions are removed from the electrolyte and are held in the electric double layers formed at the carbon aerogel surfaces of the electrodes. As the cell (30) is saturated with the removed ions, the cell (30) is regenerated electrically, thus significantly minimizing secondary wastes.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

This application is a national stage application filed under 35 U.S.C.371 of International Application PCT/US95/06553, filed May 19, 1995,which claimed priority of U.S. application Ser. No. 08/246,692, filedMay 20, 1994. This application is a Continuation-In-Part (CIP) of Ser.No. 08/246,692, now U.S. Pat. No. 5,425,858.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrochemical separation methodand apparatus for removing ions, contaminants and impurities from water,fluids, and other aqueous process streams, and for placing the removedions back into solution during regeneration.

2. Background Art

The separation of ions and impurities from electrolytes has heretoforebeen generally achieved using a variety of conventional processesincluding: ion exchange, reverse osmosis, electrodialysis,electrodeposition, and filtering. Other methods have been proposed andaddress the problems associated with the conventional separationprocesses. However, these proposed methods have not been completelysatisfactory and have not met with universal commercial success orcomplete acceptance. One such proposed ion separation method is aprocess for desalting water based on periodic sorption and desorption ofions on the extensive surface of porous carbon electrodes.

The conventional ion exchange process generates large volumes ofcorrosive secondary wastes that must be treated for disposal throughregeneration processes. Existing regeneration processes are typicallycarried out following the saturation of columns by ions, by pumpingregeneration solutions, such as concentrated acids, bases, or saltsolutions through the columns. These routine maintenance measuresproduce significant secondary wastes, as well as periodic interruptionsof the deionization process. Secondary wastes resulting from theregeneration of the ion exchangers typically include used anion andcation exchange resins, as well as contaminated acids, bases and/or saltsolutions.

In some instances, the secondary radioactive wastes are extremelyhazardous and can cause serious environmental concerns. For instance,during plutonium processing, resins and solutions of HNO₃ becomecontaminated with PuO₂ ⁺⁺ and other radioisotopes. Given the high andincreasing cost of disposal of secondary wastes in mined geologicalrepositories, there is tremendous and still unfulfilled need forreducing, and in certain applications, eliminating the volume ofsecondary wastes.

Another example is the use of the ion exchange process for industrialpurposes, such as in the electroplating and metal finishing industries.A major dilemma currently facing the industry relates to thedifficulties, cost considerations and the environmental consequences fordisposing of the contaminated rinse solution resulting from theelectroplating process. A typical treatment method for the contaminatedrinse water is the ion exchange process.

Other exemplary processes which further illustrate the problemsassociated with ion exchange include residential water softening and thetreatment of boiler water for nuclear and fossil-fueled power plants.Such water softeners result in a relatively highly concentrated solutionof sodium chloride in the drinking water produced by the system.Therefore, additional desalination devices, such as reverse osmosisfilters are needed to remove the excess sodium chloride introducedduring regeneration.

Therefore, there is still a significant and growing need for a newmethod and apparatus for deionization and subsequent regeneration, whichsignificantly reduce, if not entirely eliminate secondary wastes incertain applications. The new method and apparatus should enable theseparation of any inorganic or organic ion or dipole from any ionicallyconducting solvent, which could be water, an organic solvent, or aninorganic solvent. For example, it should be possible to use such aprocess to purify organic solvents, such as propylene carbonate, for usein lithium batteries and other energy storage devices. Furthermore, itshould be possible to use such a process to remove organic ions, such asformate or acetate from aqueous streams.

The new method and apparatus should further be adaptable for use invarious applications, including without limitation, treatment of boilerwater in nuclear and fossil power plants, production of high-puritywater for semiconductor processing, removal of toxic and hazardous ionsfrom water for agricultural irrigation, and desalination of sea water.

In the conventional reverse osmosis systems, water is forced through amembrane, which acts as a filter for separating the ions and impuritiesfrom electrolytes. Reverse osmosis systems require significant energy tomove the water through the membrane. The flux of water through themembrane results in a considerable pressure drop across the membrane.This pressure drop is responsible for most of the energy consumption bythe process. The membrane will also degrade with time, requiring thesystem to be shut down for costly and troublesome maintenance.

Therefore, there is a need for a new method and apparatus fordeionization and ion regeneration, which substitute for the reverseosmosis systems, which do not result in a considerable pressure drop,which do not require significant energy expenditure, or interruption ofservice for replacing the membrane(s).

U.S. Pat. No. 3,883,412 to Jensen describes a method for desalinatingwater. Another ion separation method relating to a process for desaltingwater based on periodic sorption and desorption of ions on the extensivesurface of porous carbon electrodes is described in the Office of SalineWater Research and Development Progress Report No. 516, March 1970, U.S.Department of the Interior PB 200 056, entitled "The Electrosorb Processfor Desalting Water", by Allan M. Johnson et al., ("Department of theInterior Report") and further in an article entitled "Desalting by Meansof Porous Carbon Electrodes" by J. Newman et al., in J. Electrochem.Soc.: Electrochemical Technology, March 1971, Pages 510-517, ("NewmanArtide"). A comparable process is also described in NTIS research anddevelopment progress report No. OSW-PR-188, by Danny D. Caudle et al.,"Electrochemical Demineralization of Water with Carbon Electrodes", May,1966.

The Department of the Interior Report and the Newman Article review theresults of an investigation of electrosorption phenomena for desaltingwith activated carbon electrodes, and discuss the theory of potentialmodulated ion sorption in terms of a capacitance model. This modeldesalination system 10, illustrated in FIG. 1, includes a stack ofalternating anodes and cathodes which are further shown in FIG. 2, andwhich are formed from beds of carbon powder or particles in contact withelectrically conducting screens (or sieves). Each cell 12 includes aplurality of anode screens 14 interleaved with a plurality of cathodescreens 16, such that each anode screen 14 is separated from theadjacent cathode screen 16 by first and second beds 18, 20,respectively, of pretreated carbon powder. These two carbon powder beds18 and 20 are separated by a separator 21, and form the anode andcathode of the cell 12. In operation raw water is flown along the axialdirection of the cells 12, perpendicularly to the surface of theelectrode screens 14, 16, to be separated by the system 10 into waste 23and product 25.

However, this model system 10 suffers from several disadvantages,including:

1. The carbon powder beds 18 and 20 are used as electrodes and are not"immobilized".

2. Raw water must flow axially through these electrode screens 14 and16, beds of carbon powder 18 and 20, and separators 21, which causesignificant pressure drop and large energy consumption.

3. The carbon bed electrodes 18 and 20 are quite thick, and a largepotential drop is developed across them, which translates into lowerremoval efficiency and higher energy consumption during operation.

4. Even though the carbon particles "touch", i.e., adjacent particlesare in contact with each other, they are not intimately and entirelyelectrically connected. Therefore, a substantial electrical resistanceis developed, and significantly contributes to the process inefficiency.Energy is wasted and the electrode surface area is not utilizedeffectively.

5. The carbon beds 18 and 20 have a relatively low specific surfacearea.

6. The carbon powder bed electrodes 18 and 20 degrade rapidly withcycling, thus requiring continuous maintenance and skilled supervision.

7. The model system 10 is designed for one particular application, seawater desalination, and does not seem to be adaptable for otherapplications.

Numerous supercapacitors based on various porous carbon electrodes,including carbon aerogel electrodes, have been developed for energystorage applications, and are illustrated in the following:

"Double Layer Electric Capacitor", Nippon Electric Co., Japanese Patentapplication No. 91-303689, 05211111.

"Electric Double-layer Capacitor", Matsushita Electric Industrial Co.,Ltd., Japanese Patent application No. 83-89451, 59214215.

Tabuchi, J., Kibi, Y., Saito, T., Ochi, A., "Electrochemical Propertiesof Activated Carbon/Carbon Composites for Electric Double-layerCapacitor in New Sealed Rechargeable Batteries and Supercapacitors",presented at the 183rd Electrochemical Society meeting, Honolulu, Hawai,May 16-21, 1993.

"Electrical Double-layer Capacitor, Uses Porous Polarized ElectrodeConsisting of Carbonized Foamed Phenol Resin", Mitsui Petrochem Ind.,Japanese Patent application No. 3,141,629.

Delnick, F. M., Ingersoll, D., Firsich, D., "Double-Layer Capacitance ofCarbon Foam Electrodes", SAND-93-2681, Sandia National Laboratory,international seminar report on double layer capacitors and similarenergy storage systems, 6-8 Dec. 1993.

Mayer, S. T., Pekala, R. W., Kaschmitter, J. L., "The Aerocapacitor: AnElectrochemical Double-layer Energy-Storage Device", J. ElectrochemicalSociety, vol. 140(2) pages 446-451 (February 1993).

U.S. Pat. No. 5,260,855 issued to Kaschmitter et al.

None of these energy storage devices is designed to permit electrolyteflow and most require membranes to physically separate the electrodes.Other electrode materials have been developed for electrolytic cells,e.g. composites of activated carbon powder and an appropriate polymericbinder, as described by Wessling et al., in U.S. Pat. No. 4,806,212.Even though such materials are made from activated carbon powders withvery high specific surface areas (600 m² /gm), much of the surface isoccluded by the binder.

Therefore, there is still a significant unfulfilled need for a newmethod and apparatus for deionization and regeneration, which, inaddition to the ability to significantly reduce, if not completelyeliminate, secondary wastes associated with the regeneration of ionexchange columns, do not result in a considerable pressure drop of theflowing process stream, and do not require significant energyexpenditure. Furthermore, each electrode used in this apparatus shouldbe made of a structurally stable, porous, monolithic solid. Suchmonolithic electrodes should not become readily entrained in, ordepleted by the stream of fluid to be processed, and should not degraderapidly with cycling. These electrodes should have a very high specificsurface area; they should be relatively thin, require minimal operationenergy, and have a high removal efficiency. The new method and apparatusshould be highly efficient, and should be adaptable for use in a varietyof applications, including, but not limited to sea water desalination.

It would be highly desirable to provide a new class of electrosorptionmedia that may be less susceptible to poisoning and degradation thancarbon-based materials, for use in capacitive deionization andregeneration methods and apparatus.

It is likely that continued direct exposure of the electrosorptionmedium to the electrolytes and chemical regenerants could furtherdegrade the electrodes. Therefore, there is a need for a new separationprocess that protects the electrosorption medium from the damagingeffect of the electrolytes and chemical regenerants, and which does notrequire the use of chemical regenerants.

Ion exchange chromatography is an analytical method which involves theseparation of ions due to the different affinity of the solute ions forthe exchanger material. It is a liquid-solid technique in which the ionexchanger represents the solid phase. In ion-exchange separation, thesolid phase or column is usually a packed bed of ion exchanger in finelycomminuted form; the anion or cation exchanger must be appropriate asthe solid phase for the sample of interest. The mobile phase is asolvent such a water with one or more additives such as buffers, neutralsalts or organic solvents.

In ion-exchange chromatography the ion-exchanging suppressor column mustbe periodically regenerated. This is a time-consuming procedure andduring the time that the stripper column is being regenerated, theapparatus is not available for use. To minimize the frequency ofregeneration, the volume ratios of the suppressor column with respect tothe separator column should be kept as low as possible, typically at aratio of 1:1. This essentially doubles the cost of the ion-exchangematerials required.

U.S. Pat. No. 4,672,042 to Ross, Jr. et al., describes an exemplaryion-chromatography system. Two separate exchange columns, anionic andcationic, are required, which increases the cost of the chromatograph,and essentially doubles the cost of the ion exchange or packing materialrequired. Solid ion exchange column packings are used, which limit theapplications of the chromatograph and require a significantly higherenergy to operate compared to a single hollow column.

Several attempts have been made to select an appropriate ion-exchangecomposition for the solid phase, e.g. U.S. Pat. No. 5,324,752 toBarretto et al.; U.S. Pat. No. 4,675,385 to Herring; U.S. Pat. No.5,294,336 to Mizuno et al.; U.S. Pat. No. 4,859,342 to Shirasawa; U.S.Pat. Nos. 4,952,321 and 4,959,153 to Bradshaw et al.

However, these devices and methods are specifically designed forparticular applications, and a single chromatograph cannot be useduniversally in various applications. Additionally, these conventionaldevices require the use of multiple columns.

Therefore, there is still a significant unfulfilled need for a new andversatile chromatograph and method of operation, which uses a singlecolumn for simultaneous anionic and cationic types chromatography. Thisnew chromatograph should control the elution time of the species beinganalyzed, should have reduced overall cost of manufacture, operation andmaintenance, should use electrical rather than chemical regeneration andshould use the same column (or stack of cells) for both anions andcations.

SUMMARY OF THE INVENTION

In one embodiment, the separation process or apparatus is used for thedeionization of water and the treatment of aqueous wastes, referred toas capacitive deionization (CDI). Unlike conventional ion exchangeprocesses, no chemicals, whether acids, bases, or salt solutions, arerequired for the regeneration of the system; instead, electricity isused.

A stream of electrolyte to be processed, which contains various anionsand cations, electric dipoles, and/or suspended particles is passedthrough a stack of electrochemical capacitive deionization cells. Eachof these cells includes numerous carbon aerogel electrodes havingexceptionally high specific surface areas (for example, 400-1000 m²/gm). By polarizing the cell, non-reducible and non-oxidizable ions areremoved from the fluid stream electrostatically and held in the electricdouble layers formed at the surfaces of the electrodes. Some metalcations are removed by electrodeposition. Electric dipoles also migrateto and are trapped at the electrodes. Small suspended particles areremoved by electrophoresis. Therefore, the fluid stream leaving the cellis purified.

In the present CDI process, energy is expended using electrostatics toremove salt and other impurities from the fluid, and, as a result, isorders-of-magnitude more energy efficient than conventional processes.Furthermore, the pressure drop in the capacitive deionization cells isdictated by channel flow between parallel surfaces of monolithic,microporous solids (i.e., the electrodes); hence, it is insignificantcompared to that needed to force water through the permeable membranerequired by the reverse osmosis process.

One feature of the CDI separation system is that no expensive ionexchange membranes are required for the separation of the electrodes.All the anodes and cathodes of the electrode pairs are connected inparallel. The system is modular, and the system capacity can beincreased to any desired level by expanding the cell(s) to inciude agreater number of electrode pairs.

Some advantages of the present invention include, but are not limited tothe following:

1. Unlike conventional processes where water is forced through amembrane by pressure gradient, or where fluid is flown through a packedbed, the CDI separation methods and systems do not require theelectrolyte to flow through any porous media such as membranes or packedbeds. In the present system, electrolyte flows in open channels formedbetween two adjacent, planar electrodes, which are geometricallyparallel. Consequently, the pressure drop is much lower thanconventional processes. The fluid flow can be gravity fed through theseopen channels, or a pump can be used.

2. The CDI system does not require membranes, which are both troublesomeand expensive, which rupture if overpressured, which add to the internalresistance of the capacitive cell, and which further reduce the systemenergy efficiency.

3. The electrodes in the CDI system are composed of immobilized sorptionmedia, such as monolithic carbon aerogel, which is not subject toentrainment in the flowing fluid stream. Thus, material degradation dueto entrainment and erosion is considerably less than in conventionalpacked carbon columns.

4. The present systems and methods are inherently and greatly energyefficient. For instance, in both evaporation and reverse osmosisprocesses, water is removed from salt, while in the present systems,salt is removed from water, thus expending less energy.

5. The present systems and methods present superior potentialdistribution in the thin sheets of carbon aerogel; most of the carbonaerogel is maintained at a potential where electrosorption is veryefficient.

The above and further features and advantages of the present inventionare realized by a new electrically regeneratable electrochemical cellfor capacitive deionization and electrochemical purification andregeneration of electrodes. The cell includes two end plates, one ateach end of the cell, as well as two end electrodes that are arrangedone at each end of the cell, adjacent to the end plates. An insulatorlayer is interposed between each end plate and the adjacent endelectrode.

Each end electrode includes an electrosorption medium having a highspecific surface area and sorption capacity. In the preferredembodiment, the electrosorption medium is formed of carbon aerogelcomposite. The cell further includes one or more intermediate electrodesthat are disposed between the two end electrodes. As the electrolyteenters the cell, it flows through a continuous open serpentine channeldefined by the electrodes, substantially parallel to the surfaces of theelectrodes. By polarizing the cell, ions are removed from theelectrolyte and are held in the electric double layers formed at thecarbon aerogel surfaces of the electrodes. As the cell is saturated withthe removed ions, the cell is regenerated electrically, thussignificantly minimizing secondary wastes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a prior art desalination system;

FIG. 2 is an enlarged schematic, isometric, elevational view of a cellused in the model desalination system of FIG. 1;

FIG. 3 is a schematic, sectional, elevational view of an electrochemicalcell;

FIG. 4A is a greatly enlarged top plan view of a capacitive electrode,adapted for use in the electrochemical cell of FIG. 3;

FIG. 4B is a greatly enlarged exploded view of a rubber gasket used inconjunction with the capacitive electrode of FIG. 4A;

FIG. 5 is a block diagram of a first embodiment of a capacitivedeionization--regeneration system using one electrochemical cell shownin FIG. 3;

FIG. 6 includes three superposed timing charts illustrating theoperation of the capacitive deionization--regeneration system of FIG. 5;

FIG. 7 is a block diagram of a second embodiment of the capacitivedeionization--regeneration system using two parallel electrochemicalcells, each formed of stacks of numerous electrodes, shown in FIG. 3;

FIGS. 8A,B,C are three timing charts illustrating the operation of thecapacitive deionization--regeneration system of FIG. 7;

FIG. 9 is a timing chart illustrating the energy saving mode of thesystem shown in FIG. 7;

FIG. 10 is a block diagram representation of a third embodiment of adeionization--regeneration system;

FIGS. 11A,B are a schematic isometric view and enlarged portion ofanother embodiment of an electrochemical cell;

FIGS. 12 through 14 represent empirical timing charts using thecapacitive deionization--regeneration system of FIG. 5;

FIG. 15 is a greatly enlarged top plan view of another electrode;

FIG. 16 is an enlarged side elevational view of the electrode of FIG.15;

FIG. 17 is a partly sectional, schematic, isometric view of a cartridge;

FIG. 18 is a top plan view of another electrode;

FIG. 19 is a cross-sectional view of the electrode of FIG. 18 takenalong line 19--19;

FIG. 20 is a cross-sectional side elevational view of yet anothercartridge or cell;

FIG. 21 is a side view of a cell formed of an electrosorption medium;

FIG. 22 is a cross-sectional view of another cell including a compositeelectrode for use in an electrochemically-regenerated ion exchangeprocess;

FIG. 23 is a block diagram of a first embodiment of an electrosorptiveion chromatograph;

FIG. 24 is a longitudinal cross sectional view of a cell used in thechromatograph of FIG. 23;

FIG. 25 is a lateral cross sectional view of a first embodiment of thecell of FIG. 24, taken along line 25--25;

FIG. 26 is a conductivity-time graph representing the elution of threespecies A, B and C separated by the chromatograph of FIG. 23;

FIG. 27 is a lateral cross sectional view of a second embodiment of thecell of FIG. 24, taken along line 25--25;

FIG. 28 is a fragmentary, top plan view of another embodiment of a cellused in a chromatograph;

FIG. 29 is an enlarged cut away, cross sectional view of the cell ofFIG. 28, taken along line 29--29;

FIG. 30 is a block diagram of an intensifier;

FIG. 31 is an isometric view of a single, monolithic, thin filmelectrode made by photolithography;

FIG. 32 is a cross-sectional view of the electrode 700 of FIG. 31 takenalong line 32--32;

FIG. 33 is a side elevational view of another electrode;

FIG. 34 is a schematic view of a tea bag electrode;

FIG. 35 illustrates a pair of tea bag electrodes of FIG. 34 placed in afluid stream within a vessel;

FIG. 36 is a schematic sectional view of an electrophoresis cell; and

FIG. 37 is a schematic view of a capacitive deionization system using amoving electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 illustrates an electrochemical cell 30 which generally includestwo oppositely disposed, spaced-apart end plates 31 and 32, one at eachend of the cell 30, and two generally identical single-sided endelectrodes 35, 36, one at each end of the cell 30, adjacent to the endplates 31 and 32, respectively. An insulator layer 33 is interposedbetween the end plate 31 and the end electrode 35. Similarly, aninsulator layer 34 is interposed between the end plate 32 and the endelectrode 36. Each single-sided electrode 35, 36 includes a single sheetof carbon aerogel composite bonded to one side of a titanium sheet witha conductive epoxy or other appropriate bonding material.

A plurality of generally identical double-sided intermediate electrodes37-43 are spaced-apart and equidistally separated from each other,between the two end electrodes 35, 36. Each double-sided electrode,i.e., 37, includes two sheets of carbon aerogel composite bonded to bothsides of a titanium sheet with conductive epoxy. While FIG. 3illustrates only seven double sided intermediate electrodes 37-43, adifferent number of intermediate electrodes can alternatively be used.For instance, the capacity of the cell 30 can accommodate at least 192intermediate electrodes, such that the total anode (or cathode) surfacearea is approximately 2.7×10⁸ cm². Ultimately, the system could beexpanded to include an unlimited number of electrode pairs.

The end electrodes 35, 36 and the intermediate electrodes 37-43 aregenerally similar in design, construction and composition, but eachintermediate electrode has two sheets of carbon aerogel composite bondedto both sides of a titanium sheet with conductive epoxy, whereas eachend electrode has only one sheet of carbon aerogel composite bonded toone side of a titanium sheet with conductive epoxy. Other porousconductive, monolithic materials can be used for the carbon aerogelcomposite.

FIG. 4A shows end electrode 35, which includes a generally flat, thinrectangularly shaped, corrosion resistant, metallic (i.e., titanium)sheet, structural support 40. A tab 42A extends integrally from one sideof the structural support 40, for connection to the appropriate pole ofa D.C. power source (not shown). A thin sheet 44 of high specific area,porous, conductive, monolithic material (i.e., carbon aerogel composite)is bonded to the surface of the structural support 40, and can be eithera cathode or an anode. The structural support 40 further includes aseries of generally identical apertures 47 for providing a passage tothe electrolyte, through the end electrode 35.

Preferably, the thin layer of high specific area material 44 is composedof a composite material formed by impregnating a carbon cloth withcarbon aerogel, wherefore, the thin layer 44 will also be referred to ascarbon aerogel composite electrode 44. The new use of this carbonaerogel composite electrode 44 relies primarily on the unique open-cellnanostructure of the carbon aerogel material, including itsinterconnected porosity, ultrafine pore sizes and huge surface area.This carbon aerogel composite material is described in more detail in anarticle entitled "Carbon Aerogel Composite Electrodes", by Joseph Wanget al., in Anal. Chem. 1993, vol. 65, pages 2300-2303, and in U.S. Pat.No. 5,260,855 by James L. Kaschmitter et al. entitled "SupercapacitorsBased on Carbon Foams". Another method of producing a porous carbon foamis described in U.S. Pat. No. 5,358,802 to Mayer et al.

Carbon aerogels are synthesized by the polycondensation of resorcinoland formaldehyde (in a slightly basic medium), followed by supercriticaldrying and pyrolysis (in an inert atmosphere). This fabrication processresults in unique open-cell carbon foams that have high porosity, highsurface area (400-1000 m² /g), ultrafine cell/pore sizes (less than 50nm), and a solid matrix composed of interconnected colloidal-likepartides or fibrous chains with characteristic diameters of 10 nm. Theporosity and surface area of aerogels can be controlled over a broadrange, while the pore size and particle size can be tailored at thenanometer scale. The carbon aerogels further offer both low density andultrasmall cell size.

The use of the carbon aerogel composite electrode 44 presents asignificant improvement over conventional devices, since in these latterdevices only part of the specific area is effective for removing ions,and the remaining area is not effective because of the potentialgradients across the electrodes. By using thin sheets of carbon aerogelcomposite as electrodes 44, substantially the entire surface area ofthese monolithic microporous electrodes is effective in the removal ofions, due to the desirable potential distribution in the aerogel.

While the best mode of the present invention utilizes thin sheets ofcarbon aerogel composite as electrodes, beds of carbon aerogel particlescan alternatively be used to form electrodes. Such beds of carbonaerogel particles have much higher specific area and sorption capacitythan beds of conventional carbon powder, and therefore they are superiorelectrodes for capacitive deionization.

In FIG. 3, the end electrodes 35, 36 and the adjacent intermediateelectrodes 37-43 are separated by means of thin sheets of insulatingmaterial, such as rubber gaskets 50-56. Each gasket has a large, squareaperture in the center to accommodate adjacent carbon aerogel compositeelectrodes 44. As shown in FIGS. 4A,B the structural support 40 includesa plurality of peripheral holes 48. When the cell 30 is to be assembled,the peripheral holes 48 are coaligned with corresponding peripheralholes in the insulation layers 33, 34 and the rubber gaskets 50-56, anda plurality of threaded rods 58, 59 are inserted through these coalignedholes, and are tightened by conventional means, such as nuts 60-63.Non-compressible, insulating, hollow, cylindrical spacers or compressionrings 50A can be inserted in the peripheral holes of the rubber gaskets50-56, and used to control the spacing of adjacent electrodes. Aplurality of compression sleeves 64A, 64B can be added to provideadditional force for sealing.

While only two threaded rods 58, 59 are shown in FIG. 3, in thisparticular example, eight threaded rods are used to tighten the cell 30to a leak proof state. These eight rods are designed to fit through theeight peripheral holes 48 in the structural support 40, as well asthrough the corresponding peripheral holes in the rubber gaskets 50-56fitted with hollow-cylindrical spacers 50A (FIG. 4B).

Once the cell 30 is assembled, a plurality of chambers 65-71 are formedbetween the end and intermediate electrodes 354 These chambers 65-71 areadapted to fluidly communicate with each other via a plurality ofapertures 73-79 in the structural supports of the intermediateelectrodes 37-43, respectively. These apertures 73-79 are not coaligned,and may be either holes or slits. They are positioned so that the fluidpath therethrough, within the chambers 65-71, is forced to flow acrossall the exposed surfaces of the carbon aerogel composite electrodes 44.In FIG. 3, the fluid first flows from left-to-right, then fromright-to-left, and so on.

In operation, and merely for illustration purposes, the anodes and thecathodes of the cell 30 are interleaved in an alternating way. In thisrespect, every other electrode is an anode, starting with the endelectrode 35, and ending with the intermediate electrode 43, and theremaining intermediate electrodes 37, 39, 41, 42 and the end electrode36 are cathodes. As such, each pair of adjacent electrodes (anode andcathode) forms a separate capacitive deionization/regeneration unit.

The stream of raw fluid or electrolyte to be processed enters the cell30 through a plurality of superposed, coaxially registered, generallycircularly or rectangularly shaped openings, including an aperture 80 inthe end plate 31, one or more apertures 82 in the insulation layer 33,and the apertures 47 in the end electrode 35. The fluid flows throughthe first chamber 65 as indicated by the arrow A, is substantiallyparallel to the electrode surface. By polarizing the firstdeionization/regeneration unit, ions are removed from the fluid streamelectrostatically, and are held in the electric double layers formed atthe carbon aerogel surfaces of the electrodes 35 and 37. This willpurify the fluid stream, at least partially.

The fluid stream then flows through the aperture 73 into the nextchamber as indicated by the arrow B, where additional ions are removedby the polarization of the second deionization/regeneration unit 81formed by the intermediate electrodes 37 and 38, thus further purifyingthe fluid stream. The fluid stream continues to travel through theremaining deionization-regeneration units, indicated by the arrows Cthrough G, and is progressively purified. Thereafter, as indicated bythe arrow H, the purified fluid stream exits the cell 30 via a pluralityof coaxially aligned apertures 90, 91, 92 in the end electrode 36,insulator layer 34, and the back plate 32, respectively.

The fluid stream leaving the cell 30 is purified since the contaminationions have been removed and collected by the cell 30. One importantcharacteristic of the novel configuration of tell 30 is that the fluidstream does not flow through the porous electrodes, but rather in anopen channel, with a relatively low pressure drop, and with minimalenergy consumption for pumping. The energy expended to operate the cell30 is minimal. In this respect, the fluid stream does not necessarilyneed to be pressurized by a pump to cause it to flow through the cell30; gravity can be used, if desired.

Also, if the inventive deionization process were used for waterdesalination, the energy expended is that which is necessary to removesalt from water, whereas in conventional desalting processes, such asevaporation and reverse osmosis, the energy is expended to remove thewater from salt. As a result, the present process is orders-of-magnitudemore energy efficient than conventional processes.

Additionally, the pressure drop in the capacitive deionization cell 30is insignificant compared to that needed for reverse osmosis. Also,contrary to conventional deionization processes, the electrodes have avery high and immobilized specific surface area and a high removalefficiency, and the carbon aerogel particles are not entrained by thefluid stream.

As the CDI cell 30 is saturated with the removed ions, the capacitiveunits become fully charged, and a sensor (not shown) indicates that suchcondition has been reached, and that the cell 30 is ready forregeneration. Contrary to conventional chemical regeneration processes,the present regeneration process is carried out electrically, thuseliminating the secondary wastes. The regeneration process takes placeby disconnecting the power supply, by interconnecting the anodes and thecathodes, by electrically discharging all electrodes 35-43, and byflowing a suitable fluid stream of water or another suitable solutionthrough the cell 30, along the same path described above in connectionwith the deionized stream of raw fluid. As a result, the capacitiveunits are discharged through, and release the previously removed ionsinto the flowing fluid stream, until the cell 30 is fully regenerated,at which time, the regeneration process is stopped and the deionizationprocess restarts. The timing control of the deionization--regenerationprocess could be manual or automated.

The overall shape and dimensions of the cell 30 are determined by themode of use and application of the CDI systems. In a preferredembodiment, the end plates 31 and 32 are identical, rectangularlyshaped, and made of 316 stainless steel or another appropriate corrosionresistant alloy. The end plates, unlike the electrodes, are notpolarized. However, other shapes can be used; e.g., if the cell 30 werecylindrically shaped, the end plates 31 and 32 are circular, or if thecell 30 were conically shaped, one of the end plates 31, 32 can have asmaller size than the other plate, and the size of the electrodestherebetween gradually increases from one end plate to the other.

The insulator layers 33 and 34, as well as 50-56 are preferably made ofan elastic, compressible, insulating, non-leachable material. Forexample, Teflon, Viton, Neoprene and similar materials are suitablematerials for specific applications.

However, other suitable materials can be used. The structural supports40 (FIGS. 4A, 4B) of the end electrodes 35, 36 and the intermediateelectrodes 37-43 are preferably made of titanium, or, alternatively theycan be selected from a suitable group of materials such as coated,corrosion-resistant, iron-chromium-nickel based alloys. Suitablecoatings include gold, platinum, iridium, platinum-iridium alloys, orother corrosion resistant materials.

In one example, the back plates are similarly sized and rectangularlyshaped, and have the following dimensions: length 8.38 cm; width 7.87cm; and thickness 0.16 cm. However, other dimensions can alternativelybe used. The tab 42A, used to make electrical connection with theelectrode, extends integrally from the structural support 40, and isgenerally, but not necessarily rectangularly shaped. In the aboveexample, the tab 42A has the following dimensions: length 1.78 cm; width2.03 cm; and thickness 0.16 cm.

As shown in FIGS. 4A and 4B, the structural support 40 includes aplurality of (in this example eight) peripheral holes 48 through whichthe threaded rods 58, 59 pass, for aligning the electrodes 35-43.Several elongated apertures 47 are shown co-aligned outside, along, andadjacent to one side 105 of the sheets of aerogel carbon composite 44.These apertures 47 are sized so as to distribute the flow uniformlyacross the sheet of carbon aerogel composite with minimal pressure drop.The number, position and size of these apertures 47 can vary with thedesired mode of use and application of the cell 30.

The carbon aerogel composite electrode 44 is shown as having a squareshape, and as being centrally positioned relative to the structuralsupport 40. In the present example, the carbon aerogel compositeelectrode 44 has a side dimension of 6.86 cm, a projected area of23.5298 cm², and a thickness of about 0.0127 cm. The electrode 44 canalso be circular, rectangular, or triangular.

While the electrode 44 is preferably made of carbon aerogel composite,any monolithic, porous solid that has sufficient electrical conductivityand corrosion resistance (chemical stability) to function as anelectrode, can alternatively be used. Such alternative materials includeporous carbon electrodes typically used in fuel cells, reticulatedvitreous carbon foams, porous metallic electrodes made by powdermetallurgy, packed columns of powder (i.e., packed beds of carbonpowder, tungsten carbide powder, various conductive oxides including tinoxide and iridium oxide), a mixture of these and other materials,electrolcatalysts such as Pt, Ir, SnO₂, or porous electrodes, that aremade by microfabrication techniques, including photolithography,electroforming, physical vapor deposition (evaporation, sputtering,etc.) and etching, and conductive sponges of any type.

The electrode 44 could also be fabricated as a packed bed of carbonaerogel particles, having significantly higher specific surface areathan the conventional packed carbon bed described in the Department ofInterior Report and the Newman Article. This design offers the advantageof greatly enhanced capacity for electrosorption of ions, adsorption oforganics, and capture of fine particles, but would require flow throughporous media.

In the example illustrated in FIG. 3, the chambers 65-71 have a volumeof about 300 ml, which corresponds to the minimum possible liquid volumerequired for regeneration. In other embodiments, the chambers 65-71 canhave different volumes, such that the minimum possible liquid requiredfor regeneration can be further reduced.

FIG. 5 illustrates a first embodiment of a capacitivedeionization--regeneration system 111 which generally includes one or astack of sequential (i.e., serial) electrochemical cells 30 (FIG. 3), anelectrical circuit 112, and a fluid circuit 114, such that the fluidcircuit 114 regulates the flow of the fluid stream through the cell 30,under the control of the electrical circuit 112.

Electrical circuit 112 includes a voltage controlled D.C. power supply117 which provides a constant D.C. voltage across the adjacent pairs ofelectrodes 35-43 (FIG. 3). A resistive load 120 and a switch 121 areconnected in parallel, across the positive and negative terminals 122A,122B, respectively, of the power supply 117, and are used to discharge,or regenerate the single electrochemical cell 30.

The electrical circuit 112 further includes a control system, as atriggering device to initiate regeneration. This control system utilizeson-line conductivity cells, ion selective electrodes, pH electrodes,polarographic sensors, impedance sensors, optical transmission cells,and light scattering sensors. The components that can be triggered bythis on-line control system include power supplies, valves and pumps.

A differential amplifier 126 is connected across a shunt resistor 118,and is further connected to an analog-to-digital converter 127 and acomputer 128. The shunt resistor 118 is used to measure the currentflowing from the power supply 117 to the cell 30, for monitoring andcontrol. The differential amplifier 126 amplifies the voltage across theshunt resistor 118 to a level that is monitorable by theanalog-to-digital converter 127 and the computer 128. Anotherdifferential amplifier 125 is connected across the terminals 122A, 122Bof the power supply 117, via the shunt resistor 118, and operates as abuffer between the power supply 117 and the analog-to-digital converter127, for protecting the analog-to-digital converter 127.

The differential amplifier 125 is connected across the terminals of thecell 30, and serves as a buffer between the cell 30 and the A/Dconverter 127. In operation, as the cell 30 is used to deionize theelectrolyte, the switch 121 is open. In order to start the regenerationprocess, the power supply 117 is turned off, or disconnected, and theswitch 121 is closed, for providing a path for the discharge current.

The analog-to-digital converter 127 is connected to the inlet stream ofthe fluid circuit 114, via a plurality of sensors, such as athermocouple 134, a conductivity probe 135, and a pH sensor 136, viarespective transducers 131, 132, 133. The thermocouple 134 enables themonitoring of the temperature of the inlet stream, in order to preventthe overheating of the electrolyte, and further enables the calibrationof the conductivity probe 135. Conductivity probe 135 is an on linesensor which monitors the conductivity of the inlet stream. The pHsensor measures the pH level of the inlet stream. The transducers 131,132, 133 convert the measurements of the thermocouple 134, conductivityprobe 135 and pH sensor 136 into voltages that are readable by andcompatible with the analog-to-digital converter 127. A flow rate meter154 measures the flow rate of the inlet stream.

The fluid circuit 114 includes a feed and recycle tank 150 whichcontains the raw fluid to be processed by the cell 30. The fluid storedin the feed and recycle tank 150 can be replaced with a continuousinflow of raw fluid. A valve 151 is fluidly connected between the feedand recycle tank 150 and a pump 152. The speed of the pump 152 is usedto control the flow rate of the inlet stream to the cell 30. The outletstream is respectively connected, via two valves 156, 157, to a producttank 160 for storing the purified fluid, and to the feed and recycletank 150. Valves 156 and 157 are used to select the mode of operation:batch mode or complete recycle; continuous mode or once through.

Similarly to the inlet stream, the analog-to-digital converter 127 isalso connected to the outlet stream of fluid circuit 114, via threetransducers 141, 142, 143, a thermocouple 144, a conductivity probe 145,and a pH sensor 146.

In the continuous mode of operation, the raw fluid or electrolyte to bedeionized is initially stored in the feed and recycle tank 150, and thevalve 157 is closed. The pump 152 is activated for pumping the fluidfrom the feed and recycle tank 150 to the cell 30, where the fluidstream is deionized and purified. The purified effluent is then routedto the product tank 160 via the open valve 156. In certain applications,it would be desirable to recycle the fluid stream more than once, inorder to obtain the desired level of purification, in which case, thevalve 156 is closed, and the valve 157 is opened, in order to allow thefluid stream to be recycled through the cell 30.

When the cell 30 is saturated, the deionization process is automaticallyinterrupted and the regeneration process starts. For this purpose, thepower supply 117 is disconnected, and a regeneration tank (not shown) isfluidly connected to the pump 152 and the cell 30. The regeneration tankcontains a suitable regeneration solution (only a relatively smallamount is needed and can have the same composition as the feed stream,for instance raw water), or alternatively, pure water can be used. Theregeneration solution is passed through the cell 30, and theregeneration process takes place by placing the removed ions back intothe regeneration solution.

In the event the electrodes become saturated with organic contaminants,it is possible to clean and regenerate the carbon composite electrode44, or other porous monolithic electrodes by passing solutions ofchemically and electrochemically regenerated oxidants, including but notlimited to Ag(II), Co(III), Fe(III), ozone, hydrogen peroxide, andvarious bleaches, through the electrochemical cell 30.

FIGS. 12 through 14 represent empirical timing charts using thecapacitive deionization--regeneration system 111 of FIG. 5.

FIG. 6 includes three superposed timing charts A, B, C, illustrating theoperation of the capacitive deionization--regeneration system 111 ofFIG. 5, used for the deionization and regeneration of 100 micromhos NaClsolution. Chart A represents the conductivity of the electrolyte, andincludes two curves, one illustrating the inlet stream conductivity andthe other curve illustrating the outlet stream conductivty. Chart Brepresents the current flowing through the cell 30. Chart C representsthe voltage across the cell 30. T represents thedeionization-regeneration cycle.

FIG. 7 illustrates a second embodiment of the capacitivedeionization--regeneration system 175 using at least two parallelelectrochemical cells 30A and 30B, both similar to the cell 30 shown inFIG. 3. FIGS. 8A,B,C show an exemplary operation of the capacitivedeionization system 175 using 100 micromhos NaCl solution. One of themain advantages of the system 175 is its ability to maintain acontinuous deionization and regeneration operation. The system 175 isgenerally similar to the system 111, and uses two cells 30A and 30B,such that when one cell 30A or 30B is deionizing the fluid stream, theother cell is regenerating, in preparation for the deionization process.Therefore, the operation of the system 175 is cyclical and continuous.For each one of the cells 30A and 30B, each cycle includes two halfcycles. The first half cycle is the deionization process, and the secondhalf cycle is the regeneration process, such that the cycles of thecells 30A and 30B are essentially 180 degrees out of phase.

The system 175 includes a power supply and switching apparatus 176connected across both cells 30A and 30B, for selectively operating thesecells. While the preferred embodiment of the system 175 includesoperating one cell for deionizing a fluid stream while the other cell issimultaneously being regenerated, both cells 30A and 30B cansimultaneously perform the same process, i.e., deionization orregeneration.

A controller 178 regulates a plurality of inflow and outflow valves 179,180a, 180b, 180c, 181a, 181b, 181c, and 182, for controlling the flow ofthe fluid stream to and from the cells 30A and 30B. An analog-to-digitalconverter 185 converts measurement signals from a plurality ofconductivity and ion specific sensors 187, 188 disposed along the fluidcircuit of the system 175, and transmits corresponding digital signalsto a computer 190, which controls the controller 178, the power supplyand switching apparatus 176, and thus the overall operation of thesystem 175. While only two sensors 187, 188 are shown, other sensors canalso be included to provide additional feedback data to the computer190.

FIGS. 8A,B,C are three timing charts illustrating the operation of thecapacitive deionization--regeneration system 175 of FIG. 7. In thiscase, no electrical power released during the regeneration of one cellis used by the other cell for deionization. FIG. 8A shows theconductivity (micromhos) versus time (seconds), of the effluent fluidstreams flowing from the cells 30A and 30B. FIG. 8B shows the current(amperes) flowing through the cells 30A and 30B. FIG. 8C shows thevoltage (volts) applied across each cell 30A, 30B. In the case ofaqueous (water-based) streams, optimum performance is obtained with avoltage pulse having an amplitude of 0.6-1.2 volts. Lower voltagesdiminish the capacity of the electrodes while significantly highervoltages cause electrolysis and associated gas evolution from theelectrodes. The solid lines in FIGS. 8A,B,C, relate to the behavior ofthe cell 30A, while the phantom or broken lines relate to the behaviorof the cell 30B.

In FIG. 8C, the solid line illustrates a series of square shaped voltagepulses 191, 192, 193 applied across the cell 30A, with a plateau valueof about 1.2 volts, while the broken line illustrates a series of squareshaped voltage pulses 194, 195 applied across the cell 30B, also with aplateau value of about 1.2 volts. It should however be understood thatdifferent voltages can be applied. Specifically, in the case of aqueousstreams, the preferred voltages range between 0.6 and 1.2 volts. Thevoltage pulses applied to cells 30A and 30B are 180 degrees out ofphase.

The voltage pulse 191 in FIG. 8C will cause the cell 30A to progresswith the deionization process, as illustrated by the current curve 197in FIG. 8B, and by the conductivity curve 198 in FIG. 8A. While thevoltage pulse 191 in FIG. 8C is applied across the cell 30A, the anodesand cathodes of cell 30B are connected together through an externalload, causing cell 30B to regenerate, as illustrated by the currentcurve 199 in FIG. 8B, and by the conductivity curve 200 in FIG. 8A.

Thereafter, the voltage pulse 194 is applied across the cell 30B causingit to progress with the deionization process, as illustrated by thecurrent curve 201 in FIG. 8B, and by the conductivity curve 202 in FIG.8A. While the pulse 194 is applied across the cell 30B, the anodes andcathodes of cell 30A are connected together through an external load,causing cell 30A to regenerate, as illustrated by the current curve 203in FIG. 8B, and by the conductivity curve 204 in FIG. 8A.

The foregoing deionization--regeneration cycle enables the system 175 tooperate continuously without interruption, since, as one of the cells30A, 30B becomes saturated, the other cell is almost or completelyregenerated, and is ready to proceed with the deionization process. As aresult, the purified fluid stream at the output of the system 175 iscontinuous. The operation of the system 175 might be particularlyattractive in nuclear power plants for scavenging contaminants fromboiler water.

To briefly summarize the operation of the system 175, during thedeionization process, the corresponding cell, either 30A or 30B,capacitively charges the electrode pairs forming it, thereby removingions from the fluid stream passing through it. At the beginning of thedeionization process, the cell has been completely and electricallydischarged; at the end of the deionization process, the cell has beencompletely and electrically charged. Subsequently, during theregeneration process, the corresponding cell, either 30A or 30B,capacitively discharges the electrode pairs forming it, thereby placingions into the fluid stream passing through it, greatly increasing theconcentration of ions in that stream. At the beginning of theregeneration process, the cell has been completely and electricallycharged; at the end of the regeneration process, the cell has beencompletely and electrically discharged.

FIG. 9 illustrates another characteristic of the present invention,namely an enhanced energy efficiency or energy saving mode. In thisparticular mode of operation, a timing chart is used to illustrate thepotential across each of the cells 30A and 30B, where the solid linesrelate to the behavior of the cell 30A, while the broken lines relate tothe behavior of the cell 30B. Starting at time t₀, the cell 30B is fullycharged and ready to be regenerated, while the cell 30A is fullydischarged and ready to begin the deionization process.

While it would be possible to disconnect the cell 30B from the powersupply 176, and to connect the power supply 176 to the cell 30A, it isnow possible to save energy, and in certain applications, save asignificant fraction of the energy required to operate the system 175.According to the present invention, at time t₀, the cells 30A and 30Bcan be connected, such that cell 30B is discharged through the cell 30A,as indicated by the curve 210, causing the cell 30A to be charged, asindicated by the curve 211. Electrical energy stored in the cell 30B isused to power the cell 30A during deionization in the cell 30A.

As soon as an equilibrium voltage is reached, i.e., approximately 0.6volts at time t₁, the cell 30A is connected to the power supply 176 sothat the charging process can be completed, as illustrated by the curve212. Simultaneously, the cell 30B is completely discharged through anexternal load, as indicated by the curve 213. As a result, a significantportion of the energy required to charge the cell 30A is generated bythe cell 30B, with the remaining energy supplied by the power supply176.

Thereafter, at time t₂, the cell 30A is fully charged and is ready forregeneration, while the cell 30B is completely discharged, and is readyfor the deionization process. The cells 30A and 30B are then connected,such that the cell 30A is discharged through the cell 30B, asillustrated by the curve 214, while the cell 30B is charged, asillustrated by the curve 215.

As soon as the equilibrium voltage is reached at time t₃, the cell 30Bis connected to the power supply 176 so that the charging process can becompleted, as illustrated by the curve 216, and the cell 30A is allowedto completely discharge through an external load, as illustrated by thecurve 217. As a result, a significant portion of the energy required tocharge the cell 30B is generated by the cell 30A, with the remainingenergy supplied by the power supply 176.

FIG. 10 illustrates a third embodiment of a deionization--regenerationsystem 220 which includes a matrix of systems 222, 224, 226 similar tothe system 175 (FIG. 7), which are connected in series. Each systemincludes at least one pair of cells which are connected and whichoperate as described in relation to the system 175. Thus, the system 222includes cells (1,1) and (1,2); the system 224 includes cells (2,1) and(2,2); and the system 226 includes cells (n,l) and (n,2). Each of thesystems 222, 224, 226 includes a power supply and switching system 176A,176B, 176C, which is similar to the power supply and switching system176 shown in FIG. 7.

In operation, when one cell, i.e., (1,1) of the pair of cells, i.e.,222, is performing the deionization process, the other cell, i.e.,(1,2), is being regenerated. While only three systems 222, 224, 226,each including two cells, are shown, a different combination of systemsor cells can be selected.

One novel application for the system 220 is the progressive andselective deionization and regeneration feature. Different potentials(V₁, V₂, V_(n)) are applied across each system (222, 224, 226,respectively) in order to selectively deionize the influent fluidstream, by having each system (222, 224, 226) remove different ions fromthe fluid stream. Thus, in this particular example, V₁ <V₂ <V_(n), suchthat the system 222 is capable of removing reducible cations such asCu⁺⁺ ; the system 224 is capable of removing reducible cations such asPb⁺⁺ ; and the system 226 is capable of removing non-reducible andnon-oxidizable ions such as Na⁺, K⁺, Cs⁺, C⁻, or other similar ions,which remain in their ionic state.

FIGS. 11A,B, represent an electrochemical cell 250, and a portion 252thereof. The cell 250 can be adapted for use as part of the capacitivedeionization-regeneration systems 111 and 175 of FIGS. 5 an 7,respectively. The cell 250 includes a plurality of electrodes 253, 254that are separated by a porous separator or membrane 255. The separator255 is sandwiched between two adjacent electrodes 253, 254, and allowsan open channel to be formed and defined therebetween. The electrodes253 and 254 are similar to the electrodes of cells 30, 30A and 30Bdescribed above. The electrodes 253, 254 and the separator 255 arerolled spirally together, so that the electrolyte flows in the openchannels formed between the electrodes 253, 254, and exits the cell 250with minimal flow resistance. While the cell 250 has been described asincluding two electrodes 253, 254 and one separator 255, additionalelectrodes and separators can be used.

FIGS. 15 and 16 illustrate another double-sided electrode 300, for usein the cells and systems described herein. While a double sidedelectrode will be described in detail for illustration purpose only, asingle-sided electrode can be designed using the same or similarconcepts.

Electrode 300 has a generally similar function to electrode 35 of FIG.4A. Electrode 300 includes a substantially flat, thin, corrosionresistant, rectangularly shaped structural support member 302, whichcomprises a dielectric board, substrate, or sheet 303. In oneembodiment, support member 302 is fabricated using printed circuit boardtechnology for replacing the more expensive metallic (i.e., titanium)structural support 40 of FIG. 4A. Thus, support member 302 may be ametallized epoxy board formed by metallizing at least part of dielectricboard 303 with a thin metallic layer or film 304. In another embodiment,dielectric board 303 includes a fiber glass epoxy board.

Metallic layer 304 may be composed of any suitable metal, such astitanium, and can be formed through alternative manufacturing processes,including sputtering the metal onto the surface of dielectric board 303and chemical vapor deposition (CVD) of metallic film or layer 304 on thesurface of dielectric board 303. The opposite side of dielectric board303 is similarly metallized with a metallic layer 306.

A tab 308 extends integrally from one side of metallic layer 304, forconnection to one pole of a D.C. power source. If tab 308 lacksstructural rigidity required for specific applications, dielectric board302 can be extended underneath tab 308 to provide the requiredmechanical support. Another tab 310 similarly extends integrally fromthe opposite metallic layer 306 to the other pole of the D.C. powersource. Both tabs 308 and 310 could also have the same polarity.

A thin sheet 314 of high specific area, porous, conductive, monolithicmaterial (e.g., carbon aerogel composite) is bonded to the surface ofmetallic layer 304. In one embodiment, sheet 314 is glued to metalliclayer 304 with an electrically conductive epoxy. Conductive sheet 314 issubstantially similar in composition to sheet 44 in FIG. 4A. Anotherthin conductive sheet 316 has a similar composition to that ofconductive sheet 314, and is bonded to the opposite metallic sheet 306.

Structural support member 302 further includes a series of generallyidentical apertures 320 for providing a passage to the electrolytethrough electrode 300, and peripheral holes 322, which are similar toapertures 47 and peripheral holes 48 in FIG. 4A.

FIG. 17 shows a cartridge 350 which includes a case 352 and a cell 355enclosed therein. Cell 355 includes a plurality of electrodess 357, 358,359, disposed in a parallel relationship relative to each other. Whileonly three electrodes are shown, a different number of electrodes may beselected.

In one embodiment, the end electrodes 357, 359 are single-sided, whilethe intermediate electrode 358 is double-sided. Electrodes 357, 358, 359may be generally similar in design, construction and composition toelectrode 300 of FIGS. 15 and 16. In another embodiment, electrodes 357,358, 359 do not include a structural support member 302. High specificsurface area, porous, conductive, monolithic materials may be used aloneas electrodes and are separated and maintained at a predetermineddistance by either dielectric spacers or placement grooves in case 352,such that adjacent electrodes, e.g., 357, 358 define channels orclearances 360 therebetween. In these embodiments, electrodes 357, 358,359 may form one or more integral cells, such as cell 355, that can beremoved from, and replaced within case 352 to form a cell or cartridge350.

In use, cell 355 is secured to, and placed within case 352, and isconnected to a D.C. power source. A fluid stream is allowed to flowfreely within channels 360, under the force of gravity, betweenelectrodes 357, 358, 359, as indicated by the arrows labeled INFLOW andOUTFLOW. The basic operation of cartridge 350 has been explained abovein relation to cell 30. A pump (not shown) may also be used. While cell355 is illustrated as having three flat electrodes 357, 358, 359, otherelectrodes of different shapes may be used. For instance electrodes 357,358, 359 may be positioned within case 352 so as to provide a serpentineflow (See FIG. 3).

One advantage presented by cartridge 350 is that cell 355, or even theentire cartridge 350, can be easily replaced for maintenance or otherpurposes. Additionally, cartridge 350 can be scaled to any desired size.Furthermore, the size and weight of cartridge 350 are reduced byeliminating the structural support 302 in FIG. 15.

FIGS. 18, 19 show two other electrodes 400, 401. Electrode 400 generallyincludes a flat, rectangularly shaped, centrally hollow, peripheralsupport member 402. Similarly, electrode 401 generally includes a flat,rectangularly shaped, centrally hollow, peripheral support member 404.Both electrodes 400, 401 are maintained at a predetermined separationdistance by means of a dielectric separator 406. While only twoelectrodes 400 and 401 may be connected to form a cell, more than twoelectrodes can be combined to form a cell.

Support members 402, 404 are generally similar in composition andconstruction. Support member 402 is made of conductive material, such astitanium, and extends integrally from one of its sides into a tab 409for connection to a pole of a D.C. power source. Support member 402 canbe formed of a metallized epoxy board. A plurality of peripheral holes410 are formed in support member 402 for assembling a cell, as before.

Electrode 400 further includes a refill cartridge 415 that fits within,and fills a central opening surrounded by peripheral support member 402.In general, cartridge 415 is rectangularly shaped, but other shapes canbe used. Cartridge 415 may include a refill member comprised of a poroussponge 417 made by powder metallurgy. Sponge 417 can be made oftitanium, platinum or other suitable metal. In a preferred embodiment,sponge 417 can be made of reticulated vitreous carbon (RVC) impregnatedby resorcinal-formaldehyde carbon aerogel. Sponge 417 is coated on itsupper and lower sides with two thin sheets 419, 420 of high specificarea, porous, conductive, monolithic material, such as carbon aerogelcomposite. Sponge 417 could also be a packed volume of particulatecarbon, carbon aerogel, or metal. Buckminster fullerene or "Bucky Balls"may also be used to fill the central opening.

Conductive sheets 419, 420 may be bonded, such as by gluing, tosubstantially the entire surface of the sponge upper and lower sides.Conductive sheets 419, 420 are electrically and physically connected tosupport member 402, so as to establish electrical contact with thecorresponding pole of the D.C. power source.

Electrode 401 is generally similar in construction and composition toelectrode 400, and includes a refill cartridge 422 coated with twoconductive sheets 423, 425. In operation, electrode 400 is connected toone pole of the D.C. power source, while electrode 401 is connected tothe other pole. A fluid stream is allowed to flow, either freely, underthe force of gravity, or under minimal pressure, through a channel 430defined between electrodes 400, 401, as indicated by the arrows labeledINFLOW and OUTFLOW. The basic operation of the cell or cartridge formedof at least electrodes 400, 401 has been explained above in relation tocell 30.

FIG. 20 shows another cartridge or cell 450 which includes at least twosubstantially similar electrodes 452, 454 that are connected to oppositepoles of a D.C. power source. Electrodes 452, 454 are maintained at apredetermined separation distance by a dielectric separator 456. Whileseparator 456 is optional, electrodes 452, 454 are not allowed to beelectrically connected.

Electrode 452 is porous and generally rectangularly shaped. Electrode452 may be made of any spongeous, foamy or porous material, such as ametal sponge or reticulated vitreous carbon (RVC) impregnated withcarbon aerogel or a similar high specific area, conductive, monolithicsubstance, in order to enhance the active surface area of electrode 452.Different electrodes may be impregnated with different compounds.

In use, cell 450 is connected to the D.C. power supply, and a fluidstream is allowed to flow, either freely, under the force of gravity, orunder minimal pressure, through electrodes 452, 454, as indicated by thearrows labeled INFLOW, FLOW and OUTFLOW. The basic operation of cell 450is similar to cell 30. The fluid stream flows through the large pores ofelectrodes 452 and 454. Carbon aerogel is used to coat the surfaces ofthe carbon foam.

Chemical regeneration may include the use of strong acids like HCl,HNO₃, H₂ SO₄, HS, so that they dissolve solid metals that have becomedeposited on the surface of the (carbon aerogel) electrode, and removeother types of scale formation. Alternatively, chemical regenerationcould include the use of strong bases capable of dissolving varioustypes of scales and impurities in order to regenerate the electrodes.

In one embodiment, a heavy organic solvent is used to dissolve heavyorganic fouling, followed by a strong chemical oxidant such as ozone,hydrogen peroxide, Fenton's reagent, silver (II), cobalt (III), iron(III), or peroxydisulfate (S₂ O₈ ⁻²). These oxidants can oxidize verythin layers of organic contaminants that have been chemisorbed to thesurface of the electrode, thereby regenerating the electrode. Thus, animportant aspect of the present invention is that the carbon electrodesare chemically resistant and regenerative. Additionally, the periodicreversal of the electrode potential will permit the electrode toregenerate very effectively. The regeneration of the electrode willprolong the effective life of the electrode and cell, and will lower themaintenance and operating cost. Periodic voltage reversal can be donewhile passing feed stream through the cell, or while passing chemicalregenerant (acid, base, etc.) through the cell.

According to the present invention, a new class of electrosorption mediamay be used in the present capacitive deionization and regenerationsystems, cells and methods. These electrosorption media are lesssusceptible to poisoning and degradation than carbon-based materials,including carbon aerogel, reticulated vitreous carbon foam and carbonpowder. They include a number of metallic carbides that can be in theform of powders, particles, foams, sponges, or porous solids made byflame spraying or powder metallurgy, sputtered thin films, or formed byother processes. These carbides include TiC, ZrC, VC, NbC, TaC, UC, MoC,WC, MO₂ C, Cr₃ C₂, Ta₂ C, and similar carbides that are stable at hightemperatures, chemically resistant, and highly conductive with aresistivity ranging between about 17 μohm-cm and 1,200 μohm-cm.

FIG. 21 shows a cell 460 that may be adapted for use in the capacitivecells and systems of the present invention. Cell 460 can be used inseveral other applications, such as in electrolyte capacitors for energystorage, and for load leveling in electric vehicles.

Cell 460 is mainly formed of two outer conductive plates 462, 463connected to a D.C. power source. Two beds 465, 466 of a powdered orgranular electrosorption medium selected from the above group, as wellas activated carbon powder and various metallic powders, are retainedagainst their corresponding plates 465, 466 by means of two porous orconductive membranes 468, 469, respectively.

A channel 470 is formed centrally between membranes 468, 469, to insurea free, unobstructed flow of fluid therethrough. The principle ofoperation of cell 460 is similar to that of capacitive deionizationcells described herein.

FIG. 22 shows another cell 475 for use in anelectrochemically-regenerated ion exchange (ERIE). Cell 475 includes twocomposite electrodes 476, 477 that define a central channel 478therebetween. Cell 475 can also be modified for use with the capacitivedeionization systems and cells disclosed herein. For example, thecomposite electrodes 476, 477 can be readily modified for use in cell 30(FIG. 3). Moreover, while central channel 478 is illustrated as astraight planar channel, it may assume various shapes and designs, e.g.a serpentine path.

Electrode 476 is a cathode while electrode 477 is an anode. Electrode476 includes an outer conductive plate 480, an electrosorptive bed 482and a polymer coating 483. Conductive plate 480 is connected to thenegative pole of a D.C. power source. Conductive plate 480 can bereplaced by a suitable structural support member, e.g. a dielectricboard, substrate, or sheet.

Bed 482 is formed of an electrosorption medium and is bonded to plate480. Alternatively, bed 482 may be retained against plate 480 by meansof coating 483. Bed 482 may be formed of any of the electrosorptionmedia described above, including but not limited to high specific area,porous, conductive, monolithic material (e.g., carbon aerogelcomposite), porous metal (e.g., titanium or platinum), pack of columnpowder, reticulated vitreous carbon (RVC) impregnated inresorcinal/formaldehyde carbon aerogel, metallic carbides that can be inthe form of powders, particles, foams, sponges, or porous solids (e.g.,TiC, ZrC, VC, NbC, TaC, UC, MoC, WC, MO₂ C, Cr₃ C₂, Ta₂ C).

Bed 482 is coated with a suitable cation exchange resin to form coating483. For example, bed 482 is dip coated in a solution of Nafion. TheNafion solution infiltrates bed 482, and upon drying, it coats theactive surface area of bed 482. The cation exchange resin may beselected from a group of polymers having negatively charged functionalgroups such as sulfonate (--SO₃ ⁻), phosphonate (--PO₃ ²⁻) and/orcarboxylate (--COO⁻). Inorganic cation exchange may also be used. Thethickness of the coating 483 is determined by the specific applicationfor which cell 475 is used.

Electrode 477 includes an outer conductive plate 485, an electrosorptivebed 487 and a polymer coating 489. Conductive plate 485 is connected tothe negative pole of a D.C. power source, and is generally similar indesign and construction to conductive plate 480. Bed 487 is alsogenerally similar in composition and construction to bed 482. Bed 487 iscoated with a suitable anion exchange resin to form coating 489. Theanion exchange resin may be selected from a group of polymers havingpositively charged functional groups such as quaternary (--NR₃),tertiary (--NR₂), and/or secondary (--NR) amines. Inorganic anionexchangers may also be used. The thickness of the coating 483 isdetermined by the specific application for which cell 475 is used.

In use, an aqueous solution with mixture of radionuclides, heavy metalsand inorganic salts is flowed through central channel 478 of cell 475.The radionuclides and heavy metals are removed from the flowing streamwith similar selectivities as conventional ion exchangers. However,unlike conventional ion exchange, no chemicals are required forregeneration since only electricity is used for the regeneration of cell475.

During the polarization of cell 475, protons (H⁺) migrate from coating483 to the interface 490 between cation exchange resin coating 483 andbed 482, and are held in the electric double layer formed at interface490. This proton migration frees active sites on coating 483 foradsorbing cations in the flowing stream. Cations (M⁺ and N⁺, e.g. Na⁺)migrate into cation exchange resin coating 483 and are held at activesites therein. Simultaneously, hydroxyl ions (OH⁻) migrate from coating489 to the interface 492 between anion exchange resin coating 489 andbed 487, and are held in the electric double layer formed at interface492. This migration of the hydroxyl ions frees active sites on coating489 for adsorbing anions in the flowing stream. Anions (X⁻ and Y⁻, e.g.Cl⁻, NO₃ ⁻, SO₄ ⁻², or CO₃ ⁻²) migrate into anion exchange resin coating489 and are held at active sites therein.

During discharge (i.e., regeneration) of cell 475, such as by shortingconductive plates 480 and 485, resin coatings 483 and 489 areregenerated, and protons and hydroxyl ions are liberated from interfaces490 and 492, respectively. These protons and hydroxyl ions displace thecations and anions (M⁺, N⁺ and X⁻, Y⁻) into a regeneration solution,such as water having the same composition as the feed stream.

Therefore, the present ionization and regeneration cell 475 and processof use minimize, if not completely eliminate the reliance on chemicalregenerants. Cell 475 can be used for deionizing boiler water for shipsand power plants, for fossil-fired and nuclear power plants, for thetreatment of mixed and hazardous wastes, for domestic and industrialwater softening, for the analysis and treatment of body fluids includingblood dialysis, and for several other applications.

Cell 475 also enables the selective, simultaneous separation of cationsand ions in a fluid or aqueous solution, with the same selectivity knownfor the ion exchange resin used as a coating. In the presentillustration, this solution contains anions X⁻ and Y⁻, and cations M⁺and N⁺. As the solution starts flowing through central channel 478certain anions and cations, i.e., X⁻ and M⁺, respectively, saturate theproximal segment 494 of electrodes 477 and 476. As the resin coatings489 and 483 in this proximal segment 494 become saturated, the remaininganions and cations, i.e., Y⁻ and N⁺ begin to saturate the distal segment495 of electrodes 477 and 476. Ionic selectivities of the ion exchangeresins, and hence the electrochemically-regenerated ion exchange (ERIE)process, are established by the relative coulombic attraction betweenvarious dissolved ions and the oppositely charged functional groups. Theforce of attraction is determined by the size, configuration, and chargeof both the ions and the functional groups.

Thus this capacitive deionization system and method present significantimprovements and advantages over other technologies. For instance,unlike ion exchange, no acids, bases, or salt solutions are required forregeneration of the system. Regeneration is accomplished by electricallydischarging the cells. Therefore, no secondary waste is generated. Sinceno membranes or high pressure pumps are required, the present systemoffers operational advantages over electrodialysis and reverse osmosis.It is more energy efficient than competing technologies, and issubstantially more energy efficient than thermal processes.

The present system can also be used to treat brackish water (800 to 3200ppm), which is very important, particularly to coastal communities.Competing technologies for the treatment of brackish water areelectrodialysis and reverse osmosis. These processes consume about 7.7Wh/gal and about 5.3 to 8.5 Wh/gal, respectively. The present system ismuch more energy efficient, and may require less than 1 Wh/gal, possibly0.2-0.4 Wh/gal, depending upon energy recovery, cell geometry, andoperation.

The system eliminates costly and troublesome membranes. A carbon aerogelCDI system has additional cost advantages over electrodialysis andreverse osmosis since expensive and troublesome membranes areeliminated.

The system also eliminates wastes from chemical regeneration. A carbonaerogel CDI system could be used for home water softening, the treatmentof hazardous and radioactive wastes, the deionization of boiler waterfor steam and power generation, and the production of ultra pure waterfor manufacturing. Industrial applications of ion exchange may require100 pounds of acid for the regeneration of one pound of cation exchangeresin, or 100 pounds of base for the regeneration of one pound of anionexchange resin. The carbon aerogel CDI system uses electricalregeneration, thereby eliminating the need for chemical regenerants andthe associated wastes.

The present system is simpler and more energy efficient than continuousdeionization which requires ion exchange resins, ion exchange membranes,and electrodes. A carbon aerogel CDI system requires only carbon aerogelelectrodes. The polymeric ion exchange media used in ContinuousDeionization are susceptible to chemical attack during the removal ofscale and fouling. Carbon aerogel is resistant to chemical attack.

A carbon aerogel CDI system is superior to beds of activated carbon.Another electrochemical process known as Electric Demineralization,described in U.S. Pat. No. 3,755,135 to Johnson, uses flow-throughpacked beds of activated carbon as electrodes. However, problemsassociated with the use of such packed beds prevented the development ofa viable commercial product. These problems included the irreversibleloss of electrosorption capacity during operation, the relatively lowspecific surface area of the activated carbon appropriate for use insuch flow-through beds, electric potential drop across beds,hydrodynamic pressure drop across beds, bed erosion due to theentrainment of carbon powder in the flowing stream, and the need forporous electrode separators. For illustration, a carbon aerogel CDIsystem with monolithic carbon aerogel electrodes offers advantages overa CDI system with flow-through packed beds of activated carbon. Slightdrops in the electrosorption capacity of carbon aerogel electrodes arealmost fully recoverable by periodic potential reversal. Thus, thesystem capacity can be maintained at a high level. Since the specificsurface area of carbon aerogel (600-1000 m² /gm) is significantlygreater than that of activated carbon powder appropriate for use in aflowthrough packed bed (230 m² /gm or 200-300 m² /gm), a greaterquantity of salt can be electrosorbed on carbon aerogel than on acomparable mass of activated carbon powder A. M. Johnson, J. Newman, J.Electrochem. Soc. 118,3 (1971) 510-517!.

It has been experimentally demonstrated that in a CDI process having 384pairs of carbon aerogel electrodes (768 individual electrodes) and atotal activated surface area of 2.4×10⁶ ft2 (2.2×10⁹ cm²), lesspotential drop occurs in a thin sheet of carbon aerogel than in arelatively deep bed of activated carbon. Consequently, more ions can beelectrosorbed on a unit of carbon aerogel surface area than on acomparable unit of activated carbon surface area. In deep packed beds ofcarbon, the potential can drop to levels where the electrosorptionprocess is not very effective. Immobilization of the carbon in the formof aerogel has made it possible to construct systems that do not requireporous membrane separators. Unlike activated carbon powder, monolithicsheets of carbon aerogel are not entrained in the flowing fluid stream.Water passes through open channels between adjacent anodes and cathodes,experiencing only a modest pressure drop of about 30 psi. In contrast,flow through a packed bed of activated carbon with comparable surfacearea experiences a significantly greater pressure drop ≧1000 psi.

The CDI system has a simple, modular plate-and-frame cell construction.Electrochemical cells required for Continuous Deionization and ElectricDemineralization are complicated by the need for particulate ionexchange resin and activated carbon, ion exchange membranes, electrodeseparators, and electrodes. The present CDI system requires simple,double-sided planar electrodes. Double-sided electrodes are made bygluing two sheets of the carbon aerogel composite to both sides of atitanium plate that serves as both a current collector and a structuralsupport. Conductive silver epoxy can be used for gluing. In oneembodiment, the carbon aerogel composite has a very high specificsurface area of 2.9-4.9×10⁶ ft² /lb (600-1000 m² /gm). Each sheet is 2.7in ×2.7 in ×0.005 in (6.86 cm ×6.86 cm ×0.0125 cm) and has a totalactive surface of approximately 3,014 ft² (2.8×10⁶ cm²). Two orificesare located along one side of the carbon aerogel electrode and admitwater to the electrode gap. A pattern of holes are located around theperimeter of the titanium plate and accommodate 12 threaded rods thathold the cell stack together. The assembly of these components into acapacitive deionization cell is also very simple. The electrodes andheaders are aligned by the threaded rods. An electrode separation of0.02 in (0.05 cm) is maintained by cylindrical nylon spacers concentricwith the threaded rods and a rubber compression seal. Even electrodesserve as cathodes while odd electrodes serve as anodes. Since theorifices in each electrode alternate from one side of the stack to theother, the flow path through the stack is serpentine. An experimentalcapacitive deionization cell configuration includes 384 pairs of carbonaerogel electrodes with a total active cathodic (or anodic) surface areaof approximately 2.4×10⁶ ft² (2.2×10⁹ cm²). However, the system can beexpanded to accommodate any desired concentration gradient across thestack, as well as any flow rate. Scale-up or scale-down for capacity andconcentration can be readily accomplished.

The present CDI system uses materials, such as carbon aerogel, that areeasy to make and commercially available. Monolithic sheets of thismaterial can be made by infiltrating a resorcinol-formaldehyde solutioninto a porous carbon paper, curing the wetted paper between glass platesin a closed vessel, and then carbonizing in an inert atmosphere. Thisfabrication process results in unique open-cell carbon foams that havehigh porosities, high specific surface areas (600-1000 M² /g), ultrafinecell and pore sizes (≦50 nm), and a solid matrix composed ofinterconnected colloidal-like particles (fibrous chains) withcharacteristic diameters of 10 nm. The porosity and surface area ofaerogels can be controlled over a broad range, while the pore size andparticle size can be tailored at the nanometer scale.

The present capacitive deionization system uses materials, such ascarbon aerogel, that are resistant to chemical attack. Fouling and scaleformation are inevitable in process equipment used for desalination.Aggressive chemical treatments are required for rejuvenation. Therefore,it would be desirable to construct the capacitive deionization systemout of materials that can withstand such chemical treatments. Carbonaerogel is relatively resistant to many of the chemicals now used forscale control, such as HCl. Unlike polymeric membranes and resins, it isalso resistant to dissolution by organic solvents. Oxidants such aschlorine attack polyamide reverse osmosis membranes, but do not appearto be a significant problem in carbon aerogel systems. Similar problemsare encountered with electrodialysis and Continuous Deionization.

The present capacitive deionization system has a fully-automatedpotential-swing operation. The Electric Demineralization process wasoperated in batch mode with no energy recovery. Capacitive deionizationcan, for instance, produce a continuous flow of product water byoperating two stacks of carbon aerogel electrodes in parallel. One stackpurifies while the other is electrically regenerated. This mode ofoperation is referred to as "potential swing" and also enables energyrecovery. For example, energy released during the discharge of one stackof electrodes (regeneration) can be used to charge the other stack(deionization). Such synchronous operation requires user-friendlyautomation.

One exemplary application of the present invention includes the designand manufacture of a deionization system for purifying radioactivewater. For instance, one embodiment of the present system could be usedto purify the waste water generated from washing fuel assemblies coatedwith metallic sodium residuals. The 500 gallons of waste water currentlygenerated during the washing of each assembly include approximately 200ppm sodium, trace quantities of other metals, trace quantities of somenon-metal that can be removed by filtration, and trace quantities ofradioactive constituents (primarily fuel cladding corrosion products).Grade B water purity would have to be achieved so that water could berecycled; (i.e., conductivity less than 20 microsiemens/cm).

FIG. 23 shows an electrosorptive ion chromatograph (EIC) 500 which canbe used for analysis, treatment and processing of various fluids and/oraqueous solutions containing a variety of anions and cations. A carriertank 510 and a pump 515 for drawing the carrier (e.g., deionized water)are connected to chromatograph 500 which includes a column 501, adetector or conductivity sensor 511, and a computer system 512. Thesolution at the output of detector 511 is collected in an effluent tank514.

Unlike conventional ion chromatography where anions are analyzed with acolumn of anion exchange resin and cations with a column of cationexchange resin, EIC 500 can simultaneously analyze both anions andcations in a single column 501 that may include one or a series ofelectrochemical cells 502, 504, 506. Column 501 replaces conventionalion exchange columns with packing material. Furthermore, the selectivityof EIC 500 can be readily changed by altering the potential between theanodes and cells 502-506, compared with conventional ion chromatographswhere selectivity is manipulated by changing the columns of ion exchangeresin or the carrier.

In use, a sample is injected into a carrier stream from carrier tank510, and passes through the single or series of cells 502-506. Each cellgenerally includes a pair of porous electrodes, i.e., an anode and acathode. These cells have an anode and/or a cathode constructedaccording to the present invention. The electrodes are polarized, anddraw ions from the flowing stream to the surface of the porouselectrodes where they are held in the electric double layers.

Each species of cation and anion has a different affinity for the porouselectrodes, and has a characteristic elution time in the cells 502-506.The elution time can be used as a basis for identifying the ions. Aconductivity sensor 511 or another type of detector at the output ofexchange column 501 is used to detect ions as they leave column 501. Theconcentration of the ions is proportional to the area under theconductivity-time (concentration-time) peak. FIG. 26 illustrates threeconductivity-time (concentration-time) peaks for three different ionicspecies A, B, C.

Computer system 512, with an analog-to-digital converter is connected todetector 511 to process data and to generate reports.

FIGS. 24 and 25 illustrate a single cell 502. In certain applicationscolumn 501 may include a single long cell. Cell 502 generally includes ahollow open ended vessel 520 which allows the sample stream to flowtherethrough in the direction of the arrows INFLOW, FLOW and OUTFLOW. InFIG. 25, vessel 520 has a rectangular cross section; however, the crosssection of vessel 520 can have other shapes, as shown in FIG. 27.

A thin sheet 524 of high specific area, porous, conductive, monolithicmaterial (e.g., carbon aerogel composite) is bonded to the inner surfaceof one side of cell 502. In one embodiment, sheet 524 is glued to cell502 with an electrically conductive epoxy. Conductive sheet 524 issubstantially similar in composition to sheet 44 shown in FIG. 4A. Sheet524 may also be bonded to at least part of the remaining three sides ofcell 502. Sheet 524 may be coated with a coating (not shown) similar tothat described in FIG. 22. Sheet 524 is connected to one pole of a D.C.power source to form an electrode. Another thin conductive sheet 526 hasa similar composition to that of conductive sheet 524, and is bonded tothe opposite, or another side of cell 502. Sheet 526 is connected to theother pole of the D.C. power source to form an electrode.

Vessel 520 and sheets 524, 526 define a central channel 530 within cell502, through which the sample stream flows. In one embodiment, channel530 is very narrow so as to minimize the amount of the sample needed. Inthis example, channel 530 is straight; however, as shown in FIGS. 28 and29, channel 530 can have other shapes, e.g. a serpentine pathway.

The general principle of operation of cell 502 has been explained abovein relation to the capacitive deionization cells and systems. As thesample stream, which includes the carrier and the sample to be analyzedor processed, passes through the first cell 502, a voltage is appliedacross anode 524 and cathode 526, which causes the various ions in thesample to be eluted at different rates. Consequently, the species areseparated.

FIG. 26 shows three species A, B and C. Species C interacts withelectrodes 524, 526 to a greater extent than species A and B, andtherefore, species C is retarded to a greater extent than species A andB. The extent of interaction between the species and electrodes 524, 526is described in terms of an adsorption or electrosorption isotherm andis quantified in terms of an equilibrium constant "K" which can becontrolled by varying the electrode material and the available electrodesurface area available for adsorbing or interacting with the ions, tocontrol the travel time of the species.

A significant advantage of the present chromatograph 500 is that theinteraction between the ionic species and the electrodes 524, 526 is anelectrostatic coulombic attraction rather than a chemical interaction.The degree of integration and the elution time can be controlled bysimply changing the voltage between the anode and the cathode. Inconventional ion chromatography, columns have to be changed to alter thedegree of interaction.

Furthermore, the present chromatograph 500 enables the use of a singlecolumn 501 for simultaneous anionic and cationic types ofchromatography. Conventional ion chromatography requires that differentcolumns be used. Additionally, this new chromatograph 500 can be usedfor separating and processing biological cells, molecules and othermatter without damage since the sample stream flows freely along channel530. Chromatograph 500 can control the elution time of various speciesbeing analyzed, and has a reduced overall cost of manufacture, operationand maintenance because of the ability to combine and implement theanionic and cationic separation processes within a single column 501.

In another embodiment, the voltage gradient across electrodes 524, 526is varied, so that the voltage is modulated or pulsed or is programmedto a desired pattern. As a result, the elution time of the species beinganalyzed can be varied, so as to minimize overlap between theconductivity-time graphs of the species. In other words, by varying theelution times of the species, the separations between the various peakson detector 511 are increased, thus making it easier to distinguish andanalyze the species.

In yet another embodiment, an ion selective electrode is used as part ofcell 506, in addition to detector 511. This ion selective electrode ispreferentially sensitive to specific ions, and may be formed ofelectrochemical cells from various forms of polarography, cydicvoltammetry, X-ray fluorescence, spectroscopy such as UV, visible,vibrational, infra-red.

FIG. 27 is a cross sectional view of cell 502 taken along line 25--25,and represents another design of cell 502. In this example, cell 502 isgenerally cylindrically shaped and has a generally circular section.Four electrodes 540-543 having similar composition to that of electrodes524, 526, are bonded to the inner surface of a vessel 545, and areseparated by four suitable insulation dividers 546-549. Each of theseelectrodes 540-543 is connected to a corresponding pole of the powersource. As shown, electrodes 540, 541 act as anodes, while electrodes542, 543 act as cathodes. The voltage gradient across one electrode pair(e.g., 540, 542) can be different from the voltage gradient across theother electrode pair (e.g., 541, 543). A cylindrical geometry would beadvantageous for applications where high pressure operation is required.

FIGS. 28 and 29 illustrate a column cell 600 which operates pursuant tothe same principles as cell 502 but differs with respect to the shape ofthe internal channel. While central channel 530 (FIG. 24) is straight,cell 600 defines a serpentine channel 601 through which the samplestream flows. Channel 601 is made as narrow but as long as possible,providing a long flow path in a small space, in order to minimize theamount of sample needed.

Cell 600 generally includes two oppositely disposed, substantially flatplates or substrates 603, 605 that are separated by an insulation layer606 of a predetermined thickness. The first plate 603 includes aserpentine trough 607, and the second plate 605 includes a similarserpentine trough 608, such that when both plates 603, 605 are connectedtogether, troughs 607, 608 and part of insulation layer 606 form channel601, which defines a serpentine pathway. Channel 601 has a single inlet610 and a single outlet 611 for the sample stream.

A thin conductive sheet 616 has a similar composition to that ofconductive sheet 524 (FIG. 24), and is bonded to the inner surface oftrough 607. A similar conductive sheet 617 is bonded to the innersurface of trough 608. These conductive sheets 616, 617 are connected tothe poles of the D.C. power supply.

The teachings described herein, particularly as to the chromatographcolumns, can also be used to design an electrochemical intensifier orconcentrator. An electrochemical intensifier is a device used toconcentrate dilute ionic solutions for subsequent measurement by any ofa variety of analytical techniques, such as ion chromatography, ionselective electrodes, differential pulse polarography.

An intensifier 650, illustrated in FIG. 30, generally includes a cellsimilar to the cells described above for the chromatographs. The porousanodes and cathodes remove ions from a relatively dilute solution 652during a capacitive charging phase. Ions are removed from the dilutesolution under the force of an imposed electric field (cell voltagegradient) and held in the double layers formed at the surfaces of theelectrodes. Subsequently, ions are collected in a more concentratedsolution 654 during a capacitive discharging or regeneration phase. Thecapacitive charging and discharging phases are as described above inrelation to the CDI systems, cells and methods.

The species that are present in the dilute solution at levels below thedetection limit of a particular analytical technique can be concentratedto a level where they become detectable. If the ions are radioactive,they can be measured as they accumulate on the porous electrodes.Similarly, X-ray fluorescence can be used to monitor heavy metals, orlike materials, that accumulate on the electrodes. A gamma ray detector655 may be used to monitor the radiation of radioactive material thataccumulates on the electrodes or in the concentrated solution 654. Ananalytical or measurement instrument 660 is connected to the effluentsolution at the output of intensifier 650, and is further connected to acomputer 665 which processes the accumulated data and controls theoperation of intensifier 650, a pump 667 that draws the dilute solution652 into intensifier 650, a valve 668 that controls the flow of theeffluent solution from intensifier 650 to the analytical instrument 660,and a valve 669 that controls the flow of the effluent to a tank 680 forstoring the solution that has been depleted of ions or deionized byintensifier 650.

FIGS. 31, 32 show a single, monolithic, thin film electrode 700 made byphotolithography. Electrode 700 has a very high specific surface areaand may replace the various electrodes described above. For example,electrode 700 may replace electrode 44 (FIG. 4A), electrodes 253, 254(FIG. 11B), electrode 314 (FIG. 15), electrode 357 (FIG. 17), electrodes419, 420 (FIG. 19), electrodes 465, 466 (FIG. 21), beds 482, 487 (FIG.22), sheets 524, 526 (FIG. 24), electrodes 540-543 (FIG. 27), and sheets616, 617 (FIG. 29).

Electrode 700 is shown as a thin, flat, porous sheet, screen or film 701made of any conductive metal, e.g., titanium, copper, platinum,tungsten, iridium, nickel or silver. The metal is selected to becorrosion resistant to the solution being processed. Using conventionalphotolithography, an array of very fine holes, i.e., 702-705 is formedon one surface of film 701. While only four holes 702-705 are shown,many more holes may be formed across the entire surface of film 701. Itwould be desirable to optimize the number of holes so as to increase thesurface area of film 701. In one example, the diameter of one hole isabout 0.1 micron, and film 701 will have a density of about 10¹⁰ holesper cm². If film 701 has a depth of about 25 microns, and holes 702-705were to penetrate through most of the thickness of film 701, thevolummetric specific surface area of film 701 would be about 64 m² /cm³.If the electrode includes a stack of ten (10) films, the volummetricspecific surface area of the electrode would be about 640 m² /cm³, whichis comparable to that of a carbon aerogel electrode.

In an electrode 700 comprised of a single film 701, holes 702-705 may ormay not extend through film 701. While film 701 is shown as a thin flatscreen, it can assume various configurations. Holes 702-705 can becylindrical with a circular cross-section, square, or of any desiredshape. Alternatively, holes 702-705 may be etched interconnectedgrooves.

FIG. 33 shows another electrode 715 which includes a stack of generallyidentical films 716-722, that are alternately interleaved with a stackof spacers 725-730. Films 716-722 are porous, and have a similarconstruction to film 701 (FIG. 31). In order for the solution toinfiltrate through the stack of films 716-722, the holes, as illustratedby a single hole 734, extend through the entire depth of films 716-722.Spacers 725-730 are thin and porous, and can be metallic or nonmetallic.In one embodiment, spacers 725-730 consist of filter papers.

It is possible to select the number of films forming electrode 715 suchthat the volummetric specific surface area of electrode 715 approachesthat of a carbon aerogel electrode, and in certain applications, it ispossible to replace the carbon aerogel electrode. An additionaladvantage of the present electrode design is that it is now possible toaccurately regulate the desired volummetric specific area of theelectrode, by either increasing or decreasing the number of constituentfilms. The films described in FIGS. 31-33 are also referred to asgraphic sheets.

FIG. 34 shows yet another embodiment of an electrode 750 called a teabag electrode. Electrode 750 includes a dosed dielectric porous bag 752that contains and restrains an electrically conductive material 753.Conductive material 753 may be any conductive powder, and in particularany one of the conductors listed herein, for example carbon aerogel. Anelectrical conductor or wire 754 extends inside bag 752 in contact withconductive material 753. When in use, wire 754 is connected to one poleof a D.C. power source.

In use, a single tea bag electrode 750 is dropped in a container 755containing a fluid 756 to be processed or analyzed. In this most basicexample, electrode 750 is positively charged and acts as an anode, whilecontainer 755 is negatively charged and acts as a cathode. As explainedabove with respect to the various CDI systems and cells, electrode 750electrosorbs the anions contained in fluid 756 inside bag 750.

Once a desired ionic concentration is reached, bag 752 is removed fromfluid 756 and processed. In one example, the concentrated ions arehazardous and bag 752 is disposed of. In another example, theconcentrated ions captured within bag 752 can be released, analyzed andprocessed. Therefore, electrode 750 can have several uses, including butnot limited to capacitive deionization and ion concentration.

Two or more tea bag electrodes of the same polarity can also be used,with the container having the opposite polarity. The container can beelectrically neutral and several tea bag electrodes 750, 760 act asanodes, while other tea bag electrodes 762, 764 act as cathodes. In thisparticular illustration the anodes and cathodes are interleaved;however, the anodes and cathodes can be placed in a variety of differentarrangements. For example, the anodes may be arranged along an outercircular pattern, while the cathodes may be arranged in a coaxial innercircular pattern. In another example, the container may be negativelycharged, and used as a cathode with the concentric circular patternsdescribed in the latter example. Other patterns may also be selected.While the number of anodes and cathodes may, in many applications, bethe same, this equality is not always required.

FIG. 35 illustrates a pair of tea bag electrodes 750, 762 placed in afluid stream within a vessel or pipe for sampling the fluid stream. Thissampling can take place periodically, at predetermined or programmedtime intervals, by the controlled application of a voltage acrosselectrodes 750, 762.

FIG. 36 shows an electrodialysis cell 800 which includes a bipolarelectrode 802 disposed intermediate a cathode 805 and an anode 807.Bipolar electrode 802 includes two films, screens, plates, etc. 808, 810disposed on either side of a conductive barrier 811. Films 808, 810 canbe any high specific surface area material, similar to the materialsdescribed above, for instance, carbon aerogel or porous carbon. Bipolarelectrode 802 acts as a central divider and defines a cathodecompartment 814 and an anode compartment 815.

In use, the electrical current flows from anode 807, through anodecompartment 815, through bipolar electrode 802, through cathodecompartment 814, toward cathode 805. For illustration purpose only, thefluid, solution or electrolyte to be processed by cell 800 is salt orsea water (NaCl+H₂ O). The solution flows from cathode compartment 814to anode compartment 815 in the direction of the arrow shown in brokenlines.

Within cathode compartment 814, the electrode reaction at cathode 805 ishydrogen (H₂) evolution, while the chloride ions (Cl⁻) precipitatetoward bipolar electrode 802 and are electrosorbed by film 808. Thisresults in an alkaline solution of sodium hydroxide (NaOH), which thenflows to anode compartment 807, where the sodium ions (Na⁺) precipitatetoward bipolar electrode 802 and are electrosorbed by film 810. Theelectrode reaction at anode 807 is oxygen (O₂) evolution. The effluentsolution consists of purified, desalted water (H₂ O).

An important advantage of cell 800 is that the salt, i.e., NaCl, orvarious radioactive salts, can be removed from the solution andimmobilized or stored within bipolar electrode 802. In one embodiment,bipolar electrode 802 may be removed and disposed of. In anotherembodiment, bipolar electrode 802 may be removed to a different locationand regenerated. In yet another embodiment, conductive barrier 811 isremoved, and the cations, i.e., sodium ions (Na+) and the anions, i.e.,chloride ions (Cl-), form a salt, i.e., sodium chloride (NaCl), whichprecipitates on the porous films 808, 810, and which is then removed andeither disposed of, or processed further.

The forgoing applications may be particularly important in the treatmentof radioactive wastes. For instance, the radioactive salts, such as CsCl(¹³⁷ Cs), may be caused to precipitate on carbon aerogel films 808, 810.The volume of these films 808, 810 can then be significantly reduced bycrushing them, or by oxidizing the carbon to form carbon dioxide.

FIG. 37 is a schematic view of a capacitive deionization system 850employing a moving electrode 852. The capacitive deionization system 850generally includes moving electrode 852 that travels between an anodecell 853 and a cathode cell 854. Moving electrode 852 includes aconductor 857 such as a wire, sheet, fluidized beads, which is supportedby, and moved by a plurality of wheels 858-863. Anode cell 853 includesa container 870, that is held at a positive potential relative toconductor 857 of moving electrode 852. Cathode cell 854 includes acontainer 872 that is maintained at a negative potential relative toconductor 857. As an example, the potential difference between the anodecontainer 870 and the moving conductor 857 is about 1.2 volts, while thepotential difference between the cathode container 872 and the movingconductor 857 is about 1.2 volts.

In this particular example, anode cell 853 contains a solution or fluid880 to be processed; however, in other applications, the solution may becontained in cathode cell 854.

In operation, the electrical current passes from container 870, throughfluid 880, to conductor 857. Consequently, the positively charged ionsin the solution 880 move to conductor 857 and are electrosorbed thereon.These ions will be carried along conductor 857 into cathode cell 854,where the electrosorbed positive ions are drawn toward the negativelycharged container 872, and are released from conductor 857 into solution881.

One advantage of CDI system 850 is that the required-actual surface areaof moving electrode 852 does not need to be relatively high, i.e., notas high as that of carbon aerogel. It is possible to increase thesurface area that solution 880 sees per unit time, by increasing thevelocity of the moving electrode 852. As a result, it is now possible toperform processes such as CDI without a high porosity electrode.

COMMERCIAL APPLICATIONS

By using the cells and systems according to the present invention, it ispossible to remove the following and other impurities and ions fromfluids, including body fluids, and aqueous streams, and to subsequentlyregenerate the cells:

1. Non oxidizable organic and inorganic anions. Inorganic anionsinclude: OH⁻, Cl⁻, I⁻, F⁻, NO₃ ⁻, SO₄ ²⁻, HCO₃ ⁻, CO₃ ²⁻, H₂ PO⁴⁻, HPO₄²⁻, and PO₄ ³⁻, In this case, the operative mechanism is electrostaticdouble layer charging. For this purpose, it would be desirable tomaintain the terminal potential across the electrodes lower than thatrequired for electrolysis of the solvent in order to avoid gasevolution. The optimum potential is in the range between 1.0 and 1.2volts, relative to the normal hydrogen electrode (NHE). In general, therecommended range of potential for water treatment lies between 0.6 and1.2 volts.

2. Non reducible cations, such as Li⁺, Na⁺, K⁺, Cs⁺, Mg⁺⁺, Ca⁺⁺. Heretoo the operative mechanism is electrostatic double layer charging.

3. Reducible cations, such as: Cu⁺⁺, Fe⁺⁺, Pb⁺⁺, Zn⁺⁺, Cd⁺⁺. In thiscase, the operative mechanism is electrodeposition.

4. Reducible anions.

5. Colloidal particles such as bacteria, viruses, oxide particles, dirt,dust. In this case, the operative mechanism is electrophoresis.

6. Chemisorption of organic molecules onto the carbon compositeelectrode 44. This adsorption process might be relatively irreversible.Regeneration in this case would involve the use of strong oxidants forthe purposes of destroying the adsorbed organics (i.e., PCB).

In particular, the present systems and cells enable theelectrodeposition of any metal, including but not limited to silver,gold, platinum, iridium, rhodium, and the removal of contaminants frombody fluids, such as blood. These contaminants could range from organicand inorganic ions to fine particles including viruses.

The present separation processes and systems have several importantapplications, including:

1. Removal of various ions from waste water without the generation ofacid, base, or other similar secondary wastes. This application may beespecially important in cases involving radionuclides, where theinventive capacitive deionization process could be used to removelow-level radioactive inorganic materials.

2. Treatment of boiler water in nudear and fossil power plants. Suchtreatment is essential for the prevention of pitting, stress corrosioncracking, and scaling of heat transfer surfaces. Such a process may beparticularly attractive for nuclear powered ships and submarines whereelectrical power is readily available and where there are spacelimitations, thereby restricting the inventory of chemicals required forregeneration of ion exchange resins.

3. Production of high-purity water for semiconductor processing. Inaddition to removing conductivity without the addition of other chemicalimpurities, the system is capable of removing small suspended solids byelectrophoresis. Furthermore, the organic impurities chemisorb to thecarbon.

4. Electrically-driven water softener for homes. The CDI system wouldsoften home drinking water without the introduction of sodium chloride,and does not require salt additions for regeneration.

5. Removal of salt from water for agricultural irrigation.

6. Desalination of sea water.

By using the CDI separation systems of the present invention, it is nowpossible to remove organic and inorganic contaminants and impuritiesfrom liquid streams by the following physiochemical processes: thereversible electrostatic removal of organic or inorganic ions from wateror any other dielectric solvent; the reversible or irreversible removalof any organic or inorganic impurity by any other adsorption process,including but not limited to underpotential metal deposition,chemisorption, and physisorption; the removal of any organic orinorganic impurity by electrodeposition, which could involve eitherelectrochemical reduction or electrochemical oxidation; and theelectrophoretic deposition and trappings of small suspended solids,including but not limited to colloids, at the surface of the electrodes.Induced electric dipoles will be forced to the electrode surfaces by theimposed electric field.

More specific applications for the CDI system and process include anyapplication where the capacitive deionizer is used to assist a gasscrubbing column; for example, if CO² were removed from a gas streaminto an aqueous stream, it would convert into HCO₃ ⁻ and CO₃ ²⁻. Theseions could be removed from the scrubbing solution by capacitivedeionization. Such applications include any large scale parallel use ofthe capacitive deionizer to assist in load leveling applications sinceit is recognized that the present invention can simultaneously serve asan energy storage device. Other applications include analyticalinstruments that combine the principles of capacitive deionization andion chromatography, and chromatographic instruments based upon ionadsorption on carbon aerogel electrodes, either monolithic or powderbeds.

The chromatographs of the present invention have various applications,including: 1. Separation and identification of amino acids, peptides,proteins, and related compounds. 2. Separation of carbohydrates andcarbohydrate derivatives. 3. Analysis of various organic acids such asaliphatic and aromatic acids. 4. Separation of aliphatic, heterocyclicand aromatic amines. 5. Separation of nucleid acid components. 6.Separation of nucleosides, nucleotides and bases, such as purine andpyrimidine bases, and mono-, di-, and triphosphate nucleotides. 7.Analysis of alkali and alkaline earth metals in the complexed anduncomplexed forms. 8. Separation of some rare earth elements. 9.Separation of halides, such as chloride, bromide and iodide. 10.Separation of phosphorous oxyanions, such as complex polyphosphatemixtures, and mixtures containing lower phosphorus anions,thiophosphates, imido-phosphates. 11. Separation of AIC components fromhemoglobin in blood. See U.S. Pat. No. 5,294,336 to Mizuno et al. 12.Separation and isolation of human plasma procoaguolant protein factorVIII from biological factors. See U.S. Pat. No. 4,675,385 to Herring.13. Analysis of Hemoglobins. See U.S. Pat. No. 5,358,639 to Yasuda etal. 14. Isolation of various constituents in blood, including but notlimited to the HIV virus.

The intensifier can be used for the analysis of various fluids,including blood and other body fluids, and aqueous solutions of organicand inorganic salts, e.g. to prove compliance with environmental laws,and for the control of plating baths used in the manufacture of printedcircuit boards.

The foregoing description of the embodiments of the present inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseforms described.

I claim:
 1. An electrically regeneratable electrochemical cell,comprising:two end plates, one at each end of the cell, the cell; twoend electrodes, one at each end of the cell, adjacent to the end plates;an insulator layer interposed between one end plate and an adjacent oneof said end electrodes; an insulator layer interposed between the otherend plate and the other one of said end electrodes; one or moreintermediate electrodes, disposed between said two end electrodes; eachend electrode and intermediate electrode including an electrosorptivemedium having a high specific surface area and sorption capacity.
 2. Theelectrochemical cell of claim 1 wherein each of said one or moreintermediate electrodes includes one or more apertures for providing alow pressure passage to a fluid through the cell.
 3. The electrochemicalcell of claim 2 wherein each pair of adjacent electrodes forms a channeladapted to fluidly communicate with a subsequent channel via said one ormore apertures in said one or more intermediate electrodes, and whereinsaid one or more apertures are not coaligned, and are positioned so thatthe fluid flowing therethrough flows across said electrosorptive medium.4. An electrochemical cell for capacitively deionizing a fluid,comprising:at least two electrodes including an electrosorptive mediumhaving a high specific surface area and sorption capacity, formed on oneor more surfaces of said at least two electrodes; each of said at leasttwo electrodes including at least one aperture; and each pair ofadjacent electrodes forming an open channel adapted to fluidlycommunicate with a subsequent open channel via said at least oneaperture to allow the fluid to flow through the cell in a serpentinepath.
 5. A cell comprising:at least two electrodes that are spaced apartand positioned in a generally parallel relationship relative to eachother for defining an open channel therebetween, and for allowing afree, unobstructed flow of fluid through said open channel; each of saidat least two electrodes being formed of a bed of electrosorptive mediumhaving high specific surface area and sorption capacity.
 6. The cell ofclaim 5 wherein one or more of said at least two electrodes includes amembrane positioned against said bed of electrosorptive medium;andwherein said membrane includes any or a combination of a porous,electrically conductive material, or a polymer coating.
 7. The cell ofclaim 5 wherein a first of said at least two electrodes includes amembrane positioned against said bed of electrosorptive medium andformed of a cation exchange resin; and wherein a second of said at leasttwo electrodes includes a membrane positioned against said bed ofelectrosorptive medium and formed of an anion exchange resin.
 8. Anelectrochemical cell comprising:a plurality of electrodes separated by aplurality of porous separators interposed between adjacent electrodes;each of said plurality of electrodes including an electrosorptive mediumhaving a high specific surface area and sorption capacity; each of saidplurality of separators defining an open fluid channel between twoadjacent electrodes; and said plurality of electrodes and separatorsbeing rolled spirally together for allowing a free, unobstructed flow offluid in said channel across said electrosorptive medium and to exit thecell.
 9. A capacitive deionization--regeneration system comprising incombination: at least two electrochemical cells of any of claims 1through 8; an electrical circuit for controlling the operation of saidat least two cells; a fluid circuit for regulating the flow of a fluidthrough said at least two cells under the control of said electricalcircuit, in order to maintain a continuous deionization and regenerationoperation.
 10. The system of claim 9 wherein said electrosorptive mediumcomprises a carbon aerogel.
 11. An electrostatic method for deionizing afluid comprising passing the fluid through a cell of any of claims 1through 8; interrupting the deionization step when said cell issaturated; and electrostatically regenerating said cell.
 12. The methodof claim 11 wherein said electrosorptive medium comprises a carbonaerogel.
 13. The electrochemical cell defined in any of claims 1 through8 wherein said electrosorptive medium comprises a carbon aerogel.
 14. Anadjacent pair of electrodes, a first electrode and a second electrode ofsaid pair each comprising: a structural support member; a conductivelayer formed on at least one surface of said support member; a sheet ofhigh specific surface area electrosorptive medium secured to saidconductive layer; and said support member including at least oneaperture for allowing a fluid to flow through the electrode and acrosssaid sheet; and wherein at least one of said at least one aperture ofsaid first electrode is not capable of coalignment with at least one ofsaid at least one aperture of said second electrode.
 15. The electrodeof claim 14 wherein said structural support member includes any of: aconductive substrate formed at least in part of any of titanium,platinum or other metal; or a dielectric substrate formed of any ofprinted circuit board material, epoxy board, or glass epoxy board. 16.An electrode comprising: a partly hollow first peripheral support memberdefining a first opening; and a first cartridge fitting, at leastpartially, within said first opening, and including: a porous conductiverefill member; and a sheet of high specific surface area electrosorptivemedium secured to said at least one surface of said refill member. 17.The electrode of claim 16 further including: a partly hollow secondperipheral support member, which defines a second opening, and which isspaced apart and maintained at a predetermined distance from said firstperipheral support member by means of a dielectric separator; and asecond cartridge which fits, at least partially, within said secondopening, and which includes: a porous conductive refill member; and asheet of high specific surface area electrosorptive medium secured tosaid at least one surface of said refill member; and wherein said firstand second cartridges define a channel therebetween, for flowing a fluidthrough said channel with minimal resistance.
 18. The electrode of anyof claims 14 through 17 wherein said electrosorptive medium is selectedfrom the group consisting of: carbon aerogel composite; a packed volumeof particulate carbon, carbon aerogel, metal, or Buckminster fullerene;a carbide or a composite of carbides that are stable at hightemperatures, chemically resistant, and highly conductive with aresistivity ranging between about 10 μohm-cm and 2000 μohm-cm, selectedfrom a group consisting essentially of TiC, ZrC, VC, NbC, TaC, UC, MoC,WC, Mo₂ C, Cr₃ C₂, or Ta₂ C; a packed volume of porous titanium,platinum or other metal; a metal sponge, or metallic foam; reticulatedvitreous carbon (RVC) impregnated in resorcinal/formaldehyde carbonaerogel; or a porous, conductive screen including an array of holes thathave been photolithographically formed to optimize the volummetricspecific surface area of said screen.
 19. The electrode of claim 18wherein said electrosorptive medium comprises a carbon aerogel.
 20. Theelectrodes of any of claims 14 through 17 wherein said electrosorptivemedium comprises a carbon aerogel.
 21. A tea bag electrode comprising: aclosed dielectric porous bag; an electrically conductive powder materialconstrained within and restrained by said bag; and a conductor extendinginside said bag in contact with said conductive powder material andproviding no constraint and no restraint for said conductive powdermaterial; said conductor and said bag being independent elements of saidelectrode.
 22. An electrode comprising: a porous, conductive screenincluding an array of holes, said holes being photolithographicallyformed to optimize the volummetric specific surface area of said screen.23. An electrochemical cell for use in a capacitivedeionization--regeneration apparatus or the like, comprising: at leasttwo electrodes of any of claims 14, 15, 16, 17, 21 or
 22. 24. Acapacitive deionization--regeneration system comprising in combination:at least two electrochemical cells of claim 23; an electrical circuitfor controlling the operation of said at least two cells; a fluidcircuit for regulating the flow of a fluid through said at least twocells under the control of said electrical circuit, in order to maintaina continuous deionization and regeneration operation.
 25. The system ofclaim 24 wherein said electrosorptive medium comprises a carbon aerogel.26. The electrochemical cell defined in claim 23 wherein saidelectrosorptive medium comprises a carbon aerogel.
 27. A capacitivedeionization system comprising in combination: an anode cell; a cathodecell; and a moving electrode including a conductor that travels betweensaid anode cell and said cathode cell.
 28. The system of claim 27wherein said electrosorptive medium comprises a carbon aerogel.
 29. Achromatograph for the analysis, treatment and processing of a fluidcontaining a variety of species including anions and cations, thechromatograph comprising in combination:a first electrically conductivemonolithic slab electrode, serving as a cathode, with a first serpentineflow path formed therein; a second electrically conductive monolithicslab electrode, serving as an anode, with a second serpentine flow pathformed therein which matches the first serpentine flow path; adielectric seal having a serpentine opening therein which matches thefirst and second serpentine flow paths; wherein the first and secondslab electrodes are stacked together with the dielectric sealtherebetween to form an enclosed serpentine flow channel; anelectrosorptive medium having a high specific surface area and sorptioncapacity in a base portion of the first and second serpentine flowpaths.
 30. The chromatograph defined in claim 29 wherein saidelectrosorptive medium having a high specific surface area and sorptioncapacity comprises a carbon aerogel.
 31. An electrochemical intensifierfor enhancing the ionic concentration in a fluid stream, comprising:acell including at least two electrodes that are polarized tosimultaneously draw and store ions present in a fluid flowingtherethrough; each of said electrodes being formed of an electrosorptivemedium having a high specific surface area and sorption capacity; anexcitation source for exciting ions accumulated on the electrodes; adetector for detecting a signal produced by the excited ions.
 32. Theelectrochemical intensifier defined in claim 31 wherein saidelectrosorptive medium having a high specific surface area and sorptioncapacity comprises a carbon aerogel.
 33. A method for operating anelectrochemical cell comprising:placing a tea bag electrode into acontainer of ionic fluid, said electrode comprising: a closed dielectricporous bag; an electrically conductive powder material constrainedwithin and restrained by said bag; and a conductor extending inside saidbag in contact with said conductive powder material and providing noconstraint or restraint for said conductive powder material; saidconductor and said bag being independent elements of said electrode;electrically charging said conductor as a cathode and said container asan anode; electrosorbing anions from said ionic fluid onto saidconductive powder material and capturing the electrosorbed anions insaid bag; and removing said bag from said ionic fluid when a desiredionic concentration of said electrosorbed anions is reached.
 34. Themethod defined in claim 33 wherein said tea bag electrode is disposableafter said removal from said ionic fluid.